uk; rainwater harvesting literature review - bradford university

A Whole Life Costing Approach for Rainwater Harvesting Systems Richard Roebuck PhD, Bradford University

Rainwater harvesting software from: www.SUDSolutions.com

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2.0 Rainwater Harvesting Literature Review

2.1 Introduction

Rainwater harvesting (RWH) primarily consists of the collection, storage and

subsequent use of captured rainwater as either the principal or as a

supplementary source of water. Both potable and non-potable applications are

possible (Fewkes, 2006). Examples exist of systems that provide water for

domestic, commercial, institutional and industrial purposes as well as

agriculture, livestock, groundwater recharge, flood control, process water and

as an emergency supply for fire fighting (Gould & Nissen-Peterson,1999; Konig,

2001; Datar, 2006). The concept of RWH is both simple and ancient and

systems can vary from small and basic, such as the attachment of a water butt

to a rainwater downspout, to large and complex, such as those that collect

water from many hectares and serve large numbers of people (Leggett et al,

2001a). Before the latter half of the twentieth century, RWH systems were used

predominantly in areas lacking alternative forms of water supply, such as coral

islands (Krishna, 1989) and remote, arid locations lacking suitable surface or

groundwater resources (Perrens, 1975). The fundamental processes involved in

rainwater harvesting are demonstrated in figure 2.1.

Figure 2.1 Flowchart demonstrating fundamental rainwater harvesting

processes

Production of runoff from catchment surface

Water storage in reservoir

Rainfall event(s)

Water use



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All rainwater harvesting systems share a number of common components

(Gould & Nissen-Peterson, 1999):

1. A catchment surface from which runoff is collected, e.g. a roof surface.

2. A system for transporting water from the catchment surface to a storage

reservoir.

3. A reservoir where water is stored until needed.

4. A device for extracting water from the reservoir.

Fewkes (2006) identifies the main uses for harvested rainwater as:

1. The main source of potable (drinking) water,

2. A supplementary source of potable water, or

3. A supplementary source of non-potable water, e.g. for WC flushing.

In developing countries the main use of harvested water is for potable supply

whilst in developed countries examples of all three uses exist, with potable

supplies being more common in rural locations and non-potable supplies in

urban areas.

2.2 A brief history of rainwater harvesting

Gould & Nissen-Peterson (1999) provide a detailed history of rainwater

harvesting systems. The authors state that, whilst the exact origin of RWH has

not been determined, the oldest known examples date back several thousand

years and are associated with the early civilisations of the Middle East and Asia.

In India, evidence has been found of simple stone-rubble structures for

impounding water that date back to the third millennium BC (Agarwal & Narain,



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1997). In the Negev desert in Israel, runoff from hillsides has been collected and

stored in cisterns to be used for agricultural and domestic purposes since

before 2000 BC (Evenari, 1961). There is evidence in the Mediterranean region

of a sophisticated rainwater collection and storage system at the Palace of

Knossos which is believed to have been in use as early as 1700 BC (Hasse,

1989). In Sardinia, from the 6th century BC onwards, many settlements collected

and used roof runoff as their main source of water (Crasta et al, 1982). Many

Roman villas and cities are known to have used rainwater as the primary source

of drinking water and for domestic purposes (Kovacs, 1979).

There is evidence of the past utilisation of harvested rainwater in many areas

around the world, including North Africa (Shata, 1982), Turkey (Ozis, 1982;

Hasse, 1989), east and southeast Asia (Prempridi & Chatuthasry, 1982), Japan,

China (Gould & Nissen-Peterson, 1999), the Indian sub-continent (Kolarkar et

al, 1980; Ray, 1983; Pakianathan, 1989), Pakistan and much of the Islamic

world (Pacey & Cullis, 1986), sub-Saharan Africa (Parker, 1973), Western

Europe (La Hire, 1742; Hare, 1900; Doody, 1980; Leggett et al, 2001a), North

and South America (McCallan, 1948; Bailey, 1959; Moysey & Mueller, 1962;

Gordillo et al, 1982; Gnadlinger, 1995), Australia (Kenyon, 1929) and the South

Pacific (Marjoram, 1987).

2.3 Rainwater harvesting in a modern context

During the twentieth century the use of rainwater harvesting techniques

declined around the world, partly due to the provision of large, centralised water

supply schemes such as dam building projects, groundwater development and



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piped distribution systems. However, in the last few decades there has been an

increasing interest in the use of harvested water (Gould & Nissen-Peterson,

1999) with an estimated 100,000,000 people worldwide currently utilising a

rainwater system of some description (Heggen, 2000).

2.3.1 Rainwater harvesting in the developed world

In the developed world the use of RWH to supply potable water is mostly limited

to rural locations, mainly because piping supplies from centralised water

treatment facilities to areas with low population densities is often uneconomic.

The development of appropriate groundwater resources can likewise be

impractical for cost reasons (Fewkes, 2006). Perrens (1982) estimates that in

Australia approximately one million people rely on rainwater as their primary

source of supply. The total number of Australians in both rural and urban

regions that rely on rainwater stored in tanks is believed to be about three

million (ABS, 1994). In the USA it is thought that there are over 200,000

rainwater cisterns in existence that provide supplies to small communities and

individual households (Lye, 1992). Harvesting rainwater for potable use also

occurs in rural areas of Canada and Bermuda (Fewkes, 2006).

The use of RWH systems to supply non-potable water to buildings in urban

areas has increased in popularity in the last 15-20 years (Fewkes, 2006).

Examples of non-potable end uses include WC flushing (Fewkes, 1999a; Bray

& Grant, 2002), urinal flushing (Cooper, 2001; Environment Agency, 2005a),

laundry cleaning (washing machines) (Ratcliffe, 2002), hot water systems

(Coombes et al, 2000c), garden/landscape irrigation (Weiner, 2003; Devi et al,



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2005), car washing (Leggett et al, 2001b) and fire-fighting (Gould & Nissen-

Peterson, 1999). Systems have been installed in a wide range of building types

including domestic properties (Leggett et al, 2001b; Day, 2002; Coombes et al,

2003a), high rise buildings (Thomas, 1998; Lau et al, 2005), schools (Bray,

2003; Paul & Bray, 2004), offices (Brewer et al, 2001), sports stadiums (Gould,

1999a; Environment Agency, 2003a), garden centres (Stephenson, 2002),

airports (Appan, 1993) and exhibition centres such as the Millennium Dome in

London (Hills et al, 1999; Lodge, 2000; Smith et al, 2000; Hills et al, 2002) and

the Eden Project in Cornwall (CIWEM, 2007).

The number of RWH systems installed varies from country to country. For

instance, in Germany during the 1990‟s the market leader alone installed over

100,000 systems, providing a total storage volume in excess of 600,000m3

(Herman & Schimda, 1999). It has been estimated that between 50,000 and

100,000 professionally designed systems are currently installed in Germany

each year (Konig, 2001; Environment Agency, 2004) and the total number of

built systems is believed to be approximately 600,000 (Leggett et al, 2001b). By

comparison, France has few installed systems. Those that do exist are often

simple, inefficient and used mainly for garden irrigation, with the domestic

utilisation of rainwater for flushing toilets and washing machines being virtually

non-existent. This low uptake is attributed primarily to the organisation of the

French water supply system which is essentially a set of regional monopolies

that have no incentive to introduce rainwater harvesting techniques since it

would reduce their profits (Konig, 2001).



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In urban locations, rainwater catchment surfaces tend to be restricted to roofs

(Hassell, 2005; Fewkes, 2006) although runoff can also be collected from other

impermeable areas such as pavements, roads and car parks. Runoff from these

areas can be more polluted than that from roof surfaces and may require a

higher degree of treatment to achieve an acceptable level of water quality

(Leggett et al, 2001b; Martin, 2001). Water storage and distribution elements

generally consist of standardised pre-manufactured components that can range

from a simple water butt with a tap at the base to more complicated systems

that can consist of underground storage tanks, filters, UV units, pumps and

automated controls. Where the latter type of arrangement is concerned, the use

of package (proprietary) systems dominates the UK market and it is possible to

purchase a complete system from a single supplier. One supplier stated that the

overwhelming majority of their domestic sales were of the proprietary type as

were most of those for commercial, institutional and industrial applications,

though bespoke systems could be designed if required (Nick Bentley of

Envireau Ltd, personal communication, June 2005).

Konig (2001) states that in the past components such as tanks, pumps and

filters were often supplied in kit form and had to be assembled on site,

necessitating the use of skilled staff and leading to increases in both installation

times and costs. Modern systems tend to be „modularised‟ and consist of

standardised mass-produced components, usually of high quality. Components

such as tanks, pumps and filters are delivered to site as complete units (no

assembly required), are easier to install and commission than the older types of

system and offer a greater degree of design flexibility. Some suppliers sell



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storage tanks with integrated filters, pump and electronic controls in what is

essentially a complete system that only requires connecting to the relevant on-

site pipework and power points.

With regards to water storage, the most common approach is to use

underground tanks (Hassell, 2005) although storage in other structures is also

possible, e.g. in the gravel sub-base of permeable driveways and pavements

(Pratt, 1995; Pratt, 1999; Leggett et al, 2001b) as well as above-ground tanks

and ponds (Woods-Ballard et al, 2007).

2.3.2 Water use in domestic, commercial and institutional buildings

The average per capita consumption for households (both metered and

unmetered) in England and Wales is currently around 150 litres per person per

day (Ofwat, 2006a). Figure 2.2 shows the water consumption share of different

micro-components in a typical UK domestic household (POST, 2000). The

diagram shows that not all of the water used in a household needs to be of

potable quality, particularly water used for WC flushing (31%), washing machine

(20%) and outside supply (4%). Potentially, about 55% of the potable mains

water used within a typical UK household could be replaced with another source

such as rainwater, provided that it was of a suitable quality for the intended

uses.



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Figure 2.2 Water consumption by micro-component for a typical UK

household (Adapted from POST, 2000).

Water usage patterns are different in office buildings compared to domestic

dwellings. WC and urinal flushing are often major consumers of water and can

account for up to 63% of water use, as shown in figure 2.3. As with domestic

properties, there is no specific need for this water to be potable and it could

potentially be substituted with rainwater provided that an adequate quality at the

point of use was achieved.



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Figure 2.3 Average water use in office buildings

Adapted from Leggett et al (2001a), p23.

2.3.3 Common drivers for RWH in the developed world

Most developed countries rely heavily on centralised water treatment and piped

distribution systems in order to provide a safe and reliable supply to the public.

Jeffrey & Gearey (2006) state that modern consumers have come to expect a

„right‟ to clean water, with infrastructure developments focusing on meeting

consumer demand with little restraint on quantity or quality. This has led to the

development of water delivery systems that supply excess water at excess

quality for the uses to which much of it is put, e.g. using potable water for toilet

flushing and garden watering. Increases in demand are typically met by further

resource development (Howarth, 2006). For instance by the construction of new

reservoirs, enlargement of existing ones and/or the development of further

groundwater resources (Lallana et al, 2001). However, in some countries this

approach has begun to present a number of difficulties. For example, Germany

relies to a large extent on groundwater for its public water supply which has led

to over-extraction, lowering of the water table and adverse environmental



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effects. Pollution of groundwater resources is also becoming a potential public

health risk (Sayers, 1999). Hiessl et al (2001) questions whether the continued

reliance on the centralised treatment and supply paradigm is the optimal choice

given the substantial operating/maintenance costs involved and increasingly

stringent environmental legislation.

The use of RWH systems in Germany has in recent years been promoted as

part of the solution to addressing these problems, with many city councils

providing incentives and subsidies to encourage their installation (Herrmann &

Schmida, 1999). Konig (2001) documents the use of RWH in a wide variety of

building types in Germany. Other potential benefits include the (so far

theoretical) ability to offset the development of new water resources (Schilling &

Mantoglou, 1999), reduce peak flow volumes and lower the risk of urban

flooding from the predominantly combined sewer system (Vaes & Berlamont,

2001).

In Sweden, increasing urbanisation and the widespread use of large-scale

centralised treatment has resulted in a supply system that is vulnerable to

shortages and has also contributed to water quality deterioration. Research has

indicated that demand management measures, including RWH for non-potable

uses, could help to reduce the amount of water required from the public supply

system for urban developments (Villarreal & Dixon, 2005).

In Australia there is a move towards Integrated Urban Watershed Management

(Mitchell, 2004; Roon, 2006), also known as Water Sensitive Urban Design



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(WSUD) (Argue et al, 2003). This approach involves considering the urban

water cycle as an holistic whole rather than as distinct separate entities (i.e.

stormwater, floodwater, wastewater and sources of potable water) with one of

the goals being to harvest and reuse stormwater in order to augment the mains

supply (Argue, 2001). Research has indicated that, as well as lowering reliance

on mains water, RWH has the potential to reduce the volume of stormwater

disposed of to the sewer system, reduce peak runoff rates (Coombes et al,

2001) and be economically viable at both the development and regional scales

(Coombes et al, 2000a, b).

Buildings that contain a water meter and in which the owners/occupiers are

charged for the water they use on a volumetric basis may be able to reduce

their water bills through the installation of a RWH system (Shaffer et al, 2004).

Whether or not this is a cost effective option depends on a number of factors,

including the capital cost of the RWH system, operation/maintenance expenses,

the volume of mains water that can be supplanted by harvested water and the

assumed lifetime of the system (Leggett et al, 2001b).

Rainwater harvesting may also have a role to play in promoting sustainable

urban water management. The EU Water Framework Directive (WFD), which

came into force in all member states in December 2000, calls for a range of

measures to be taken in order to protect the aquatic environment (EC, 2000).

The primary objectives of the WFD include a requirement to:



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Prevent further deterioration, and protect and enhance the status of

aquatic ecosystems, with regards to their water needs, terrestrial

ecosystems and wetlands (Article 1(a)).

Promote the sustainable use of water based on long-term protection of

available water resources (Article 1(b)).

Contribute to mitigating the effects of floods and droughts (Chave, 2001).

The literature suggests that RWH is potentially able to contribute towards the

achievement of each of these goals in a number of ways: by reducing reliance

on centralised water treatment and distribution systems that appropriate water

from the natural environment; lessening instances of urban flooding by reducing

both the volumes of water disposed of to the sewer system and peak flow rates

within sewers; by providing a water supply “buffer” in times of drought. Similarly,

other EU Directives have objectives that RWH could help to meet. For example,

the EU Habitats Directive (EC, 1994) requires that sites of European

conservation interest achieve favourable conditions by 2010. To achieve these

aims water abstractions in some areas may need to be reduced to a more

sustainable level (Environment Agency, 2005b), leading to increased pressure

on remaining supply sources. It is conceivable that the wider uptake of RWH

and similar technologies could to some extent mitigate the effects of reducing

permissible abstraction levels.

The rest of this review focuses on the types of rainwater harvesting systems

used in urbanised areas of the developed world for non-potable applications.

Systems suitable for use in domestic, commercial, institutional, public and



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industrial buildings for applications such as WC and urinal flushing, washing

machines and outdoor use (e.g. garden/landscape irrigation, vehicle washing)

are discussed but not industry-specific applications such as process or cooling

water. Particular attention is given to the use of proprietary („package‟ or „off-

the-shelf‟) RWH systems within the UK as these currently dominate the market

for urban installations in this country. The use of water butts is not considered

as these have limited potential for curbing reliance on mains water, peak flow

reduction or for reducing the volume of stormwater discharged to the sewer

system (Woods-Ballard et al, 2007). Relevant UK legislation and regulations are

discussed were appropriate. This information should not be assumed to apply

outside of this country.

2.4 Types and configurations of RWH systems

Three basic types of system for supplying non-potable water to buildings for

internal and external uses are identified by Leggett et al (2001b): directly

pumped, indirectly pumped and gravity fed. A number of variations are given by

Herrmann & Schmida (1999) and Konig (2001). External use only systems are

also available and these are essentially direct systems that can only be used for

outdoor purposes, such as garden watering and vehicle washing. In all cases,

water is collected from a catchment surface and held in a sealed storage

structure until needed. Once harvested water has been used, for example to

flush the WC, it is considered to be in the same effluent category as potable

water would be if used for the same purpose, e.g. harvested water used to flush

a WC becomes foul (black) water, the same classification that applies to potable



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water once it has been used to flush a WC. The resulting effluent is treated in

the same manner regardless of the initial source.

2.4.1 Indirectly pumped systems

Rainwater is initially held in a storage tank and then pumped to a header tank

within the building, which is usually located within the roof void. Water is

delivered to appliances via gravity and the header tank should be at least one

metre above the supply points. If the storage tank runs dry, the header tank is

supplied with top-up water from the mains. If the storage tank is full, any

additional incoming water will exit via an overflow and will normally be disposed

of either to a soakaway/infiltration device or sewer. See figure 2.4 for a

schematic of an indirectly pumped RWH system.

The main advantages of indirectly pumped systems are that if the pump fails

(e.g. due to mechanical/electrical failure or power loss) then water will still be

supplied to the associated fixtures and fittings via the mains top-up function.

Low cost pumps and simple controls are possible and systems tend to be

energy efficient as the pump runs at full flow (Environment Agency, 2007).

The main disadvantages are that they tend to deliver water at low pressures.

This can lead to slow filling of WC cisterns and the system may not provide

enough pressure to work with some appliances. Some proprietary units solve

the low pressure problem by using a hybrid system. Water for the WC is gravity

fed from a header tank which also has mains top-up whilst water for the

washing machine and garden is delivered via a pump at equivalent mains



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pressure. The advantage with this arrangement is that in the event of a power

failure it is still possible to flush the toilet. Indirect systems also require the use

of a header tank (Environment Agency, 2007). These can add to the overall

cost of a system (though not usually significantly) and there may not always be

sufficient space in the roof void to site the tank (Hannah Reid of Stormsaver Ltd,

personal communication, June 2007).

Figure 2.4 Schematic of an indirectly pumped RWH system

Adapted from Leggett et al (2001b), p38.

External use

Mains top-up

Overflow

Soakaway/infiltration device or sewer

Collection guttering

Cross flow filter

Rainfall

Storage tank

Pump

Supply

Overflow

Header tank

Key

Usable water

Discarded water

Manhole cover

Grey/black water to foul sewer system



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2.4.2 Directly pumped systems

In a directly pumped system (sometimes also referred to as a pressurised

system) rainwater is initially held in a storage tank and then pumped directly to

the point of use when required, e.g. to WC cisterns and washing machines.

There is no header tank with a direct system and mains top-up occurs within the

storage tank. Mains top-up does not completely fill the tank but maintains a

minimum level that is able to meet short-term demand. If the storage tank is full,

any additional incoming water will exit via an overflow and will normally be

disposed of either to a soakaway/infiltration device or sewer. Figure 2.5 shows a

schematic of a directly pumped RWH system.

The main advantages of directly pumped systems are that water is provided at

mains pressure which is ideal for garden hoses and washing machines, and

that they do not require a header tank (Environment Agency, 2007).

The main disadvantages are that if the pump fails (e.g. due to

mechanical/electrical failure or power loss) then no water can be supplied. WCs

would have to be flushed manually (e.g. using a bucket of water) and washing

machines would not function. Mains top-up controls can also be more

complicated than with indirect and gravity fed systems (Environment Agency,

2007).



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Figure 2.5 Schematic of a directly pumped RWH system


2.4.3 Gravity fed systems

Gravity fed systems differ from the direct and indirect variants primarily in that

the main storage tank is located within the roof void of the building. Rainwater is

collected from the roof, filtered and then piped directly to the storage (header)

tank. Water is delivered to appliances via gravity and the storage tank should be

at least one metre above the supply points. Mains top-up water is supplied

directly to the tank if it runs dry. If the tank is full, any additional incoming water

will exit via an overflow and will normally be disposed of either to a

soakaway/infiltration device or sewer.

External use



Cross flow filter

Rainfall

Storage tank

Pump

Supply

Overflow

Mains top-up

Key

Usable water

Discarded water

Manhole cover




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The main advantages of gravity fed systems are that they do not require a

pump or electrical supply as is the case with the direct and indirect versions

(Fewkes, 2006). Also, since there is no pump, there is no risk of pump-

associated supply failure.

The main disadvantages are that the water pressure is likely to be less than that

of the mains supply. This can result in poor performance of some appliances,

e.g. slow filling of WC cisterns, and some appliances such as some modern

washing machines may stop working altogether. In this case a pump may be

required to boost the water pressure (Leggett et al, 2001b). There may also be

issues with high structural loads, damage from leaking components and water

quality issues due to fluctuating temperatures in the stored water (Fewkes,

2006). It also has to be possible to collect runoff from the roof, filter it and

deliver it to the tank under the action of gravity. In this case the relative levels of

the various components (roof, filter and tank) are critical and it may not be

possible to find an arrangement that functions hydraulically (Fewkes, 1989).

See figure 2.6 for a schematic of a gravity fed RWH system.



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Figure 2.6 Schematic of a gravity fed RWH system


2.4.4 Selection of system type for domestic and commercial applications

Direct systems are usually recommended for use in domestic properties since

there is not always sufficient space in the building‟s roof void for the header tank

that indirect and gravity systems require. Also, direct systems have been found

to be better at providing the required flow rate of water (Hannah Reid of

Stormsaver Ltd, personal communication, June 2007). For commercial

situations, indirect (header tank) systems are generally recommended. One of

the primary reasons is that peak demands can be relatively high compared with

domestic situations. Consequently, if a direct system was used then the pump

may not be able to supply the required water at a sufficient rate, resulting in low

External use

Mains top-up

Overflow



Cross flow filter

Rainfall

Supply

Tank

Key

Usable water

Discarded water




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flow and low pressure at the points of use. The header tank also acts as a

failsafe in the event of pump failure as water can still be supplied via gravity to

the WCs and urinals. This enables the premises to remain open in the event of

pump failure. Header tanks also ease demand on the pump, enabling units to

be used that operate at lower flow rates. This increases pump reliability and life

expectancy (Hannah Reid of Stormsaver Ltd, personal communication, June

2007).

2.5 Components of RWH systems

Proprietary systems can consist of a number of different components, some

specific to the RWH aspects and some which are part of the building but are

utilised as part of the rainwater system (auxiliary components). A list of typical

RWH-specific components could include some or all of the following items:

First-flush diverters.

Filters.

Storage device, e.g. tank.

Overflow arrangement (including backflow prevention device).

Pump and associated components.

UV unit.

Electronic controls/management systems.

Header tank (for indirect and gravity fed systems).

Mains top-up arrangement.

Distribution pipework.



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A list of auxiliary components could include some or all of the following items:

Guttering and collection pipework.

Catchment area, e.g. roof.

Figure 2.7 shows a range of common rainwater harvesting and auxiliary

components and demonstrates how they can be integrated in order to create a

complete system. The diagram shows an indirect system with a header tank but

most of the components could equally apply to a direct system as well.

Figure 2.7 Schematic showing range of common RWH system

components

Mains top-up with type AA/AB air gap

Overflow Collection guttering

Coarse filter

Storage tank

Pump

Non-potable supply

Overflow

First flush diverter


Soakaway/ infiltration device

or sewer

Catchment area

In-line filter(s)

Backflow prevention device

Electronic controls

UV unit

Potable (mains) water supply

Water meter

Potable supply

Header tank

In-tank filter

Key

Usable water

Discarded water

Solenoid valve



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2.5.1 First flush diverters

During dry periods roofs become contaminated with a variety of pollutants such

as atmospheric particulates, bird droppings, leaves and other debris (Cunliffe,

1998; Fewkes, 2006). When it rains, some of the contaminants are washed off

the catchment surface and transported in the runoff flow. The rainfall intensity

and number of dry days preceding a rainfall event significantly affects the

quality of the runoff, with long dry periods resulting in higher pollutant loads for a

given catchment (Gould & Nissen-Peterson,1999).

Research has shown that the initial „first flush‟ of runoff is more polluted than

subsequent flows and that the concentration of contaminants associated with a

given rainfall event tend to reduce exponentially with time. Therefore, diverting

the initial portion of runoff generated by a storm away from the storage device

will mean that the quality of water entering storage is improved and the need for

subsequent treatment reduced or even eliminated altogether (Wu et al, 2003;

Martinson & Thomas, 2005).

As a rule of thumb, for each millimetre of first flush collected the contaminate

load will be about half the amount present in the previous millimetre (Martinson

& Thomas, 2005). Figure 2.8 shows sketches of a range of commonly used first

flush diverter types. All involve the diversion and temporary storage of the initial

portion of runoff. The „interceptor‟ and „splitter‟ variants rely on filling a container

with the first flush and slowly releasing it via a throttled outflow. The majority of

subsequent runoff from the catchment surface bypasses the first flush container



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and is routed into the tank. The „pit‟ variant works on a similar principle except

that outflow from the first flush container is into the ground via infiltration.

Gould & Nissen-Peterson (1999) state that the use of first flush diverters tends

to be limited and when they are used they often suffer from a lack of

maintenance. As a result of this neglect many function incorrectly or have

simply been disconnected by the building occupiers. Research conducted by

Coombes (2002) implies that the use of first flush diverters is fairly common in

Australia. However, Konig (2000) suggests that collecting the initial flush of

water is unnecessary for non-potable applications. Herrmann & Schmida (1999)

make no mention of diverters when discussing treatment processes for roof

runoff intended for non-potable uses in Germany. Mustow et al (1997) state that

the inclusion of such a device can increase the costs and complexity of a

system without providing any significant benefit. Limited evidence was found for

the use of first flush diverters in the UK and none of the proprietary system

suppliers provide them as a standard part of their package systems.



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Figure 2.8 Cross-sectional sketches of typical first flush diverters

2.5.2 Filters

It is recommended that rainwater be filtered before entry into the storage tank in

order to remove debris such as leaves, grit, moss and soil. Leggett et al (2001b)

identify a range of filter types and sub-types. Filters should be easy to clean (or

self-cleansing) and should not block easily (Martinson & Thomas, 2003). With

regards to contemporary systems, the use of crossflow filters is essentially

ubiquitous and these are described in more detail below. Cartridge filters are

First flush splitter (Adapted from Che et al, 2003)

Outflow

Inflow

Throttled first flush outlet

Container for holding

first flush

First flush interceptor (Adapted from Ntale, 2003)

Inflow Outflow

Throttled first flush outlet

Container for holding

first flush

Buoyant sphere, creates watertight seal when container is full

Outflow Inflow

Debris screen Concrete baffle

First flush passes through holes in base of box into infiltration chamber

Reinforced concrete box

First flush infiltrates into ground

First flush pit (Adapted from Coombes, 2002)



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often employed in systems that have a UV unit. These are also discussed

further.

Crossflow filters

Crossflow filters contain a mesh screen which water flows across (hence the

name) and that separates the flow into two fractions. The portion that passes

through the mesh is cleaned of all debris larger than the mesh size (typically

0.2-1.0mm) and passes to the storage tank. The residual debris is washed from

the mesh by the remaining fraction of water and diverted away from the tank,

e.g. to the sewer system or an infiltration device. Crossflow filters are

considered to be self-cleansing since debris is automatically washed from the

mesh screen.

Figure 2.10 shows two types of commonly installed crossflow filter

configurations. One is a downpipe filter in which the mesh sits adjacent to the

pipe wall. Water running down a vertical pipe at atmospheric pressure mostly

flows down the inside wall and downpipe filters take advantage of this

phenomenon by intercepting the flow and filtering the majority of it. Vortex filters

(which are usually located underground) use the momentum of the incoming

flow to create a vortex effect, swirling the water around the inside of the filter

casing which is lined with a fine mesh. Water is forced through the mesh,

filtering out debris and sending the processed water to the storage tank. As with

the downpipe version, the unfiltered water and associated debris are diverted

away from the tank.



33

Figure 2.9 Cross-sectional sketches of typical crossflow filters

German best practice recommends the use of filters with porosities in the range

of 0.2-1.0mm with no further filtration required for non-potable uses (Konig,

2001). Self-cleansing filters are preferred as they require less maintenance and

reduce the cost of consumables (Leggett et al, 2001b).

Filter casing

Downpipe crossflow filter (Adapted from Leggett et al, 2001b)

Downpipe

Filter mesh

Filtered water to tank

Debris and unfiltered water

Filtered water to tank

Incoming water

Debris and unfiltered water

Filter casing

Vortex action

Filter mesh

Vortex crossflow filter (Adapted from Leggett et al, 2001b)

Incoming water



34

Cartridge filters

Cartridge filters are usually placed after the storage tank and require that water

be passed through them under pressure. They are most often used in systems

that require a high degree of water quality and low turbidity, such as those that

include a UV unit or for potable applications. It is common practice to have

several arranged in series with the unit that has the largest porosity first in line

and subsequent units arranged according to diminishing pore size, e.g. 25μm

followed by 5μm. Cartridge filters tend to have small porosities and so pre-

filtration is required, for example by the prior use of a screen or crossflow

device. If this is not done then they will rapidly clog. They are not self-cleansing

and so require replacement at regular intervals, typically every 3 months or

thereabouts (Leggett et al, 2001b).

Other types of filter

Leggett et al (2001b) also describe a number of other filter types including in-

tank floating, screen, slow sand, rapid gravity, reed beds, membrane and

activated carbon. Chemical disinfection is also mentioned as another option for

improving water quality. Way & Thomas (2005) describe an experimental

system in which a slow sand filter was integrated into the actual rainwater tank.

However, with the exception of in-tank floating filters, none of these methods

would appear to have achieved any significant degree of penetration in the UK

market and none of the RWH system suppliers offered them as part of their

regular package deals. Therefore they are not discussed further in this thesis.



35

2.5.3 Rainwater storage devices

A storage device is required to collect and hold catchment runoff because

rainfall events occur more erratically than system demand (Fewkes, 2006).

Water storage capacity is required in order to balance out the difference

between supply and demand (Gould & Nissen-Peterson, 1999). In the

developed world the most commonly used storage device is the underground

tank (Hassell, 2005). Other types of reservoir structures exist, such as above

ground tanks and ponds (Woods-Ballard et al, 2007), the gravel sub-base of

permeable driveways and pavements (Pratt, 1995; Pratt, 1999; Leggett et al,

2001b), covered flat roofs (Mustow et al, 1997), the void space beneath

garages (Courier, 2002; Jones, 2002), geo-cellular structures (Stephenson,

2002) and small local aquifers (Argue et al, 1998; Coombes et al, 2000c;

Gardner et al, 2001). However, the use of storage devices other than

underground tanks appears to be limited in the UK, particularly within the

domestic market and so these alternative approaches are not considered

further.

Installing tanks underground has a number of advantages: it helps to prevent

algal growth by shielding the tank from daylight (Konig, 2001), protects the tank

from extreme weather conditions at the surface such as freezing spells (Leggett

et al, 2001b) and helps to regulate the water temperature in the tank, keeping it

cool and limiting bacterial growth (Fewkes & Tarran, 1992).

Storage tanks come in a variety of shapes and sizes and can be constructed

from a range of materials including concrete, ferrocement, bricks, steel and



36

plastics such as glass reinforced plastic (GRP) or high-density polyethylene

(Leggett et al, 2001b; Fewkes, 2006). Some are relatively basic in design whilst

others are essentially complete systems that incorporate the tank, filters, pump

and mains top-up arrangement in a single integrated unit. Tanks for domestic

systems generally have storage volumes in the 1-10m3 range. Tanks for

commercial systems are available in a wider range of sizes and can be tens or

hundreds of cubic metres in size. Vessels can also be linked together to provide

additional volume meaning that there is no theoretical upper limit on the amount

of storage space that can be provided, site constraints not withstanding. Figure

2.10 shows examples of the types of underground tanks that are available.

For a given tank the purchase and installation costs are related to the storage

capacity (Fewkes, 1997) and so it is important to select a tank with an

appropriate volume. There is a balance between cost and performance which

has to be judged carefully. Determining the optimum tank volume is a key

aspect of this thesis and is covered in more detail in chapters five, six and

seven. Whichever tank is selected, current best practice recommends that it

should be sized such that it overflows at least twice per year in order to facilitate

the removal of any floating debris (Fewkes, 2006).



37

Figure 2.10 Examples of underground storage tanks

2.5.4 Storage device overflow arrangement

Modern rainwater tanks have an overflow arrangement in order to prevent

localised flooding if the capacity of the tank is exceeded, and also to help avoid

stagnation of stored water and remove floating debris. The overflow can be

connected to a soakaway/infiltration device, storm drain or combined sewer

system but not a foul sewer (Leggett et al, 2001b). It must include an anti-

backflow device in order to prevent contaminated water entering the tank in the

Moulded plastic tank (Courtesy of Freewater UK)

Ground level

Sectional concrete tank (Adapted from Leggett et al, 2001b)

Sealed joints to ensure tank

integrity

Lockable manhole cover

Sectional concrete rings

Inflow

Integrated tank system (Courtesy of Rainharvesting Systems Ltd)

Inflow

Filtered flow

Overflow

Ground level

Complete concrete tank (Adapted from Konig, 2001)

Filter screen (basket)

Lockable manhole cover



38

event of downstream surcharging (DCLG, 2006a, part 1.70b). Overflows are

predominantly unrestricted (no throttle) and water passes through them via

gravity flow although pumped overflows are also available.

2.5.5 Pumps

RWH systems require that stored rainwater be pumped either to the point of use

(direct systems) or to a header tank located at least 1m above the point of use

(indirect systems). In general, gravity fed systems do not require a pump since

water is fed straight from the catchment surface to a high-level storage tank.

However, they are sometimes used with gravity systems in order to increase the

water pressure which may otherwise be too low to work with certain appliances,

e.g. some modern washing machines.

Pumps have a finite lifespan and will require repair/replacement at some point,

typically after 5-10 years of use. It is also recommended that they are checked

at least once per year in order to ensure that they are functioning correctly

(Leggett et al, 2001a).

2.5.6 UV units

Ultraviolet (UV) radiation is effective at killing a wide range of waterborne

bacteria and viruses. UV disinfection has a number of advantages: ease of use,

requires no chemicals, short retention time, no effect on the chemical

characteristics, taste or odour of the water, maintenance is not onerous, and

there is no risk from excessive use as might be the case with chemical

treatments (McGhee, 1991). UV disinfection of potable water supplies has been



39

shown to be sufficient for the inactivation of 99.9% of most microorganisms

(Hall et al, 1997).

UV units can be fitted to RWH systems in order to safeguard water quality.

However, in order for a UV unit to effectively kill microorganisms the water has

to have a low turbidity, necessitating the use of fine filters (e.g. a 25μm filter

followed by a 5μm filter, located in series before the UV unit). If this is not done,

suspended solids in the water can effectively shield harmful pathogens from UV

light and they may not be destroyed (Crittenden et al, 2005; Parsons &

Jefferson, 2006). The use of a UV unit will add to the capital and running costs

of a system. Extra filters are required and these need replacing every six

months or so. The UV bulb consumes electricity and also has a finite lifespan,

generally requiring replacement after about six months of use (Leggett et al,

2001b; Shaffer et al, 2004). UV units fitted to RWH systems tend to be passive,

i.e. they do not control the rate of flow through them. Rather, the capacity of the

pump should be matched to the treatment flow rate of the UV unit.

In the normal mode of operation, the UV unit is left permanently on as

constantly switching it on and off as demand dictated would significantly shorten

the life of the bulb. Power consumption for domestic units is typically in the 15-

55W range and lamps generally last for between 8,000-10,000 hours of

continuous use (Crittenden et al, 2005), which equates to about twelve months.

Prolonged use can reduce the UV output intensity and so it is recommended

that lamps be replaced after a maximum of 10,000 hours even if they are still



40

functional (Krishna et al, 2005). Figure 2.11 shows a schematic of a typical UV

disinfection unit.

Figure 2.11 Schematic of a UV disinfection unit


In the UK there is currently no legal requirement for a RWH system to

incorporate a UV unit and the literature did not provide any definitive guidance

on when and where one should be used. One supplier stated that UV

disinfection is not necessary and was primarily introduced into the UK market in

order to reduce the perceived risks associated with harvested water, thereby

encouraging its use (Glyn Hyett of 3P Technik, personal communication, 22nd

April 2006). Another stated that they would only recommend UV treatment in

special cases and that coarsely filtered rainwater was of sufficient quality for

toilet flushing and irrigation purposes and did not normally require further

treatment (Lutz Johnen of Aqua-Lity, personal communication, 24th April 2006).

Water in

Irradiated water out

Control panel

UV lamp



41

2.5.7 Electronic control and management units

Many contemporary RWH systems have the option of including an electronic

control and management unit. This is not essential and some systems can be

controlled using simple mechanical float valves and a low-level switch to trigger

the pump. However, more sophisticated controls allow for the use of float

switches, pressure sensors and electrically actuated valves which can result in

better overall performance (Leggett et al, 2001b). Controls can also have visual

readouts of systems status, such as the level of water in the tank, or report if

there is a problem such as pump failure, disinfection failure or filter blockage

(Konig, 2001). A significant fraction of the proprietary systems currently for sale

in the UK come supplied with electronic controls as standard.

Electronic controls consume electricity and so will add to system running costs,

although power consumption is generally low. They also have a finite lifespan

and will likely need replacement after 15-20 years (Lutz Johnen of Aqua-Lity,

personal communication, 24th April 2006)

2.5.8 Header tank

Indirect systems require the use of a header tank. This is normally located in the

roof void of the building and should be at least 1m above the point of supply.

High and low level switches are used to signal the storage tank pump when to

activate and when to disengage. If mains top-up occurs in the header tank then

this is usually controlled by a low level switch in conjunction with a solenoid or

float valve (Leggett et al, 2001b).



42

2.5.9 Mains top-up arrangement

Given the intermittent nature of rainfall it is rare that a RWH system can be

designed such that a constant supply of harvested water can be guaranteed. In

times of shortfall it is advisable to have a top-up arrangement which can supply

enough mains water to meet short-term demand. Top-up can be provided in a

number of locations. In an indirect system it most commonly occurs in the

header tank, although it can also be in the storage tank. Direct systems

normally have mains top-up in the storage tank although a variation exists

known as a “centralised” system in which the pump and mains top-up are

integrated into a single unit located inside the building. If the main storage tank

runs empty, mains water is fed into the suction pipe of the pump and from there

water is transferred directly to the point of use (Woods-Ballard et al, 2007). Top-

up controls can consist of simple mechanical valves controlled by flotation

devices or more complicated systems involving float activated switches coupled

with solenoid valves.

2.5.10 Solenoid valves

Solenoid valves are typically used to start/stop the mains top-up function. A float

activated switch, located either in the header tank (for indirect and gravity fed

systems) or primary storage tank (for direct systems), triggers the valve if the

water volume falls below a predetermined level. This activates the mains top-up

function, ensuring that a minimum amount of water is available at all times.

Once the minimum water level has been restored, the float activated switch

closes the valve, shutting off the flow of mains top-up water.



43

Solenoid valves have a typical life expectancy of between 5 and 10 years

(Leggett et al, 2001a). The power consumption of solenoid valves suitable for

use in RWH systems is low, typically in the range of 2-5W and they only

consume power when operating (Jerry Cook of Red Dragon Valves Ltd,

personal communication, 25th May 2007) so running costs can be expected to

be minimal.

2.5.11 Distribution pipework

A pipe distribution network is required to transport water from the storage tank

to the point of use and a wide selection of pipes are available that are suitable

for this task. Further information on appropriate pipe materials and installation

protocols can be found in The Water Supply (Water Fittings) Regulations 1999

(HMSO, 1999), WRAS (1999a) and Leggett et al (2001b). Plastic pipes are

commonly used. These are durable and, if installed correctly, have a long

service life although they will require replacement at some point, typically after

about 20 years of use (Leggett et al, 2001a).

2.5.12 Guttering and collection pipework

Rainwater runoff from the catchment surface needs to be collected and diverted

to the rainwater storage device. If the catchment surface is a roof then collection

is generally via a system of gutters feeding into one or more downpipes and

from there into the storage device. For further information refer to HMSO (1999,

2000a) and WRAS (1999a).



44

2.5.13 Catchment surface

In urban locations the most commonly utilised catchment areas are roofs

(Hassell, 2005; Fewkes, 2006) although runoff can also be collected from other

impermeable areas such as pavements, roads and car parks (Environment

Agency, 1999a). Not all of the rain falling on a catchment area can be collected

as some is lost from the system due to processes such as depression storage

and evaporation (Wilson, 1990; Butler & Davies, 2004). Other factors that also

influence the amount of lost water include the rainfall depth and intensity,

antecedent conditions, the material the catchment is made from and the

catchment slope (Li et al, 2004).

The effective runoff is the volume of rainwater falling on the catchment that can

be collected and routed into the collection network of gutters and pipes. When

estimating the effective runoff volume, a commonly used approach is to employ

a dimensionless runoff coefficient that represents the observed losses from the

catchment compared with an idealised catchment from which no losses occur

(Fewkes, 2006). The effective runoff is calculated by multiplying the volume of

rain falling on the roof by the coefficient. A coefficient value of 0 would mean

that no runoff occurs whilst a value of 1 would mean that all the rain falling on

the catchment is translated into effective runoff. Examples of runoff coefficients

for a variety of different roof types are given in Leggett et al (2001b) and are

reproduced below in table 2.1. This data is based on the long-term experience

of German RWH system manufacturers



45

Table 2.1 Common roof runoff coefficients


Surface Type Coefficient

Roof Pitched roof tiles 0.75-0.90 Flat roof, smooth surface 0.50 Flat roof with gravel layer or thin turf (<150mm) 0.40-0.50

2.6 Water quality

In the UK, for harvested water intended for potable uses the Private Water

Supplies Regulations (1991) apply (Leggett et al, 2001a). By contrast, there are

currently no legally binding quality criteria for water derived from reuse systems

(rainwater and greywater) intended for non-potable uses (Roaf, 2006). Kim et al

(2007) state that in order for water systems to become more sustainable the

quality of the water supplied should correspond to the intended applications.

This practice will help to identify alternative sources that can be utilised where

demand is for non-potable water. The same principle has also been proposed

by a number of other authors, e.g. Alegre et al (2004); Sakellari et al (2005).

The information presented thus far in this chapter has demonstrated that

rainwater can be used for a number of non-potable applications such as WC

flushing, washing machines, garden irrigation and vehicle washing. None of

these uses involve the (intentional) consumption of harvested water. It could

therefore be argued that standards less stringent than those required for

potable water would be acceptable for non-potable uses such as these.

In the UK a range of water quality guidelines and recommendations exist for

rainwater harvesting systems. Some of these are derived from monitoring

studies conducted on RWH systems, such as those monitored as part of the



46

„Buildings That Save Water Project‟ (Brewer et al, 2001). Others are based on

existing standards such as the European Union (EU) Bathing Water Directive

and World Health Organisation (WHO) recommendations. Mustow et al (1997)

recommend that quality guidelines should be application specific and propose

different „categories of use‟, each with different quality requirements depending

on the likely degree of human exposure. Leggett et al (2001b) state that the

greatest risk of microbiological contamination occurs when water is ingested or

deliberately sprayed, creating an aerosol. Thus uses such as surface crop

irrigation and vehicle washing would require a higher level of water quality than,

for example, subsurface irrigation and toilet flushing. A sample of

recommendations found in the literature that relate to non-potable uses are

summarised in table 2.2. Most of the information relates to microbiological

quality since this is often considered to be the criteria of most concern when

dealing with water reuse systems (WROCS, 2000).



47

Table 2.2 Summary of recommended microbiological water quality

standards for non-potable applications

Reference

Uses

Key indicators

Threshold values

WHO (1989) Irrigation of crops likely to be eaten uncooked, sports fields, public parks

Faecal coliform per 100ml

≤1000

Irrigation of public lawns with which the public may come into contact, e.g. hotel lawns

Faecal coliform per 100ml

≤200

Leggett et al (2001b)

Washing machines Total coliforms per 100ml E.coli per 100ml

0, or counts less than 10/100ml acceptable providing not in consecutive samples 0

WRAS (1999a) Toilet flushing Faecal coliform per 100ml Faecal enterocci per 100ml

<10,000 <100

EC Bathing Water Quality Directive (76/160/EEC)

Toilet flushing Total coliforms per 100ml Faecal coliform per 100ml

<10,000 <2,000

Most non-potable use guidelines are less strict than those applicable to potable

water supplies and allow for the presence of some bacteriological organisms.

WRAS (1999a) make the point that most people are exposed to literally millions

of faecal organisms whilst performing everyday activities and that for harvested

water to add to the burden of exposure the faecal coliform content would need

to be in excess of 10,000 per 100ml. Leggett et al (2001b) state that where



48

rainwater from a catchment with low contamination is used for WC flushing,

washing machines and irrigation, and the system is well designed and operated,

then disinfection is not necessary and should not be applied. For single-user

installations (which includes domestic systems serving only one property) that

are intended for WC flushing, irrigation and other non-potable uses Shaffer et al

(2004) consider that coarse filtration and settlement provide satisfactory

treatment. For multi-user installations (commercial and domestic systems

serving several properties) the same criteria are recommended with the addition

that disinfection to achieve a total coliform count <1,000 colony forming units

(cfu) per 100ml should be applied if thought to be necessary. The United States

Environmental Protection Agency (USEPA, 1992) and WHO (1989) guidelines

also allow for some degree of microbiological contamination as does the EU

Bathing Water Directive (76/160/EEC). Konig (2001) states that in well designed

and operated systems only coarse filtration prior to entry into the storage tank is

required and that the risk to human health from non-potable applications is

minimal.

In light of the above information it was decided that water quality would not be

explicitly considered in the thesis. It was assumed that adequate quality can be

maintained for non-potable uses providing that, in line with the previous

recommendations, rainwater undergoes coarse filtration prior to entry into the

storage tank. The use of UV sterilisation may be considered in some instances

but for domestic situations it was assumed that the use of UV is not necessary.



49

2.7 Contemporary rainwater harvesting in the UK

Compared to countries such as Germany the UK lags behind in the application

of RWH technology and it has been estimated that by the turn of the millennium

only between 1,000 and 2,000 systems had been commissioned (Hassell, 2001;

Leggett et al, 2001b). However, the market is growing and at the time of writing

it is reported that approximately 400 systems per year are being installed

(UKRHA, 2007). The majority of system sales in the UK currently originate from

member companies of the UK Rainwater Harvesting Association (UKRHA). This

organisation is a focus group established in 2004 in order to help coordinate the

activities of the private sector, disseminate information about and promote

RWH, liaise with the Government and also contribute towards the research and

development of RWH technology. They currently have 14 full members and it is

believed that these represent about 75% of the UK market, which at the end of

2006 was estimated to be worth over three million pounds (Terry Nash of

Freerain™, personal communication, February 12th 2007).

2.7.1 Barriers to the uptake of RWH systems

Roaf (2006) discusses the barriers for water conservation and reuse in the UK

from the perspective of a range of stakeholders and actors, including central

government & regulators, local authorities, water companies, private

consultants, architects, developers & planners, manufacturers, and customers &

consumers. The key points raised that are of relevance to rainwater harvesting

systems have been summarised in table 2.3. A more detailed discussion can be

found in Roaf (2006), pages 221-233.



50

Table 2.3 Summary of key barriers to the uptake of RWH systems in UK

Adapted from Roaf (2006), pp221-233.

Stakeholder(s) Key barriers

Central Government and regulators

Lack of water quality standards; lack of empirical data on which to base quantitative risk models; unwillingness of any Government or regulatory body to take responsibility for setting and monitoring standards

Local authorities Lack of knowledge by managers, council members, planners, building control officers and environmental health officers; poor communication between departments, lack of information regarding RWH system costs, maintenance requirements and water quality standards

Water companies Profit motive for investing in water efficiency measures is low; industry focus is on reducing consumer costs not on creation of a sustainable water supply system; water sector in general lacks imagination, prefers single product mindset (mains supply) rather than multi-product mindset of which RWH could be a part

Private consultants

Water efficiency currently seen as a poor relation to energy efficiency in terms of earning potential; lack of good quality information on the economics of water conservation and reuse; lack of clear standards; lack of a developed market for associated products

Architects, developers and planners

General lack of knowledge and awareness; additional costs of construction and maintenance associated with water conservation and reuse systems; lack of current water quality standards; lack of a common technical language with which engineers, planners and architects can discuss water related systems

Manufacturers Difficulty in achieving and maintaining reliable level of water quality; no established water quality standards; lack of an established market for water related products; uncertainty surrounding expected service life of systems; pioneering status of much of the technology; lack of good quality research with which to inform technology development

Customers and consumers

UK does not have an established culture of water conservation; consumers tend to be reactive in their habits; low availability of good quality information; current low value of mains water; aversion to what may be seen as „experimental‟ technology; water quality issues

A number of other researchers have investigated or considered barriers to

uptake. These are summarised in table 2.4.



51

Table 2.4 Further barriers to the uptake of RWH systems in UK

Reference Identified barriers

Brewer et al (2001); Leggett et al (2001a,b)

Unproven cost benefit, difficulties in operation and maintenance, lack of water quality standards and associated public health concerns, unproven technology and lack of guidance

Grant (2006) Cost effectiveness of systems, particularly domestic, is questionable

Woods-Ballard et al (2007)

Potential risk to public health, possible expense and complexity of installation, above ground tanks can be unsightly

Brown et al (2005) Cost of water rarely a driver for the end-user but cost of installing a RWH system may be seen as significant

2.7.2 Public perception and acceptability

One of the key factors in the success or otherwise of any water reuse scheme is

the perception of the users and the acceptability to them of the existing or

proposed technology. It is important that the social and cultural aspects of water

use are considered when planning and designing such systems (Jeffrey &

Gearey, 2006). Past failure to adequately take into account and address public

concerns has led to the cancellation of a number of potentially beneficial reuse

schemes (DeSena, 1999).

A review of the relevant literature was undertaken and the main results are

summarised in table 2.5. The information presented in this table shows that

there is little public opposition against, and some considerable support for, the

use of harvested water for non-potable applications such as toilet flushing,

laundry washing and garden irrigation. Generally speaking, the less personal or

intimate the use, the higher the level of acceptability. The assumption is

therefore that the use of RWH systems for non-potable applications, such as

those considered in this thesis, would not be hampered in any significant way

by opposition from the general public.



52

Table 2.5 Summary of key findings relating to the public perception

and acceptability of non-potable RWH systems

Reference(s) Key findings

WPCF, 1989; WROCS, 2000; Hills et al, 2003; Lazarova, 2003

Toilet flushing generally most readily accepted use for recycled water. Acceptability found to decline as use becomes more „personal‟, i.e. as direct human contact becomes more likely

Bruvold, 1985 Uses such as WC flushing are preferred to more intimate uses such as food preparation and cooking

Brewer et al, 2001 Little concern reported over use of harvested water for WC flushing

McDaniels et al, 2000

Aesthetics (e.g. colour, odour and turbidity) impact upon the willingness to use recycled water, although these indicators may not necessarily be a reliable guide to actual water quality

Jeffrey, 2002; Jeffrey & Gearey, 2006

People are generally more accepting of the use of recycled water in their own homes than they are in public or institutional buildings

Leggett et al, 2001b If RWH systems are to become successful in the domestic market then their reliability will need to be comparable to that of other domestic systems such as hot water appliances

Hills et al, 1999, 2002

Investigation into performance and public perception of a combined greywater, rainwater and groundwater system at the UK Millennium Dome. Out of >1,000 users interviewed, 95% agreed that such systems were appropriate for use in public areas

BMRB, 2006 Telephone survey in which 473 UK homeowners were asked various questions regarding their water use habits and opinion of RWH systems. 92% agreed that RWH was “a good idea” and 30% stated that they would be more likely to buy a house if it had a RWH system already installed. 63% stated that they would be most likely to install a system for financial reasons (e.g. reduced water bills)

2.7.3 Drivers and potential benefits of RWH systems

In the UK as elsewhere there is an emerging consensus that the traditional

centralised and disparate approach to the urban water cycle is neither optimal

nor sustainable (Argue, 2001; Hiessl et al, 2001; Maheepala et al, 2003, 2004;

Anderson, 2005; Sakellari et al, 2005; Stacey, 2005; Roon, 2006). Historically,

the primary aim has been the promotion of economic growth and the urban

water cycle has essentially been compartmentalised with water supply, storm



53

drainage and wastewater treated as separate entities. This approach has led to

the overexploitation of water resources and environmental damage (Geiger,

1995). Pratt (1995) identifies a range of problems currently facing the UK water

sector:

1. In some parts of the country water demand is exceeding the available

supply.

2. Resources that are available are not always located in areas of demand.

This can result in the distribution of water over large distances (Fewkes,

2006).

3. Low flows in rivers due to over-abstraction.

4. Increased capital investment in water reclamation works has not always

led to a corresponding improvement in receiving water quality.

5. The expansion of urban areas has resulted in increased runoff volumes

and peak flow rates, negatively impacting river geomorphology, aquatic

habitats and water quality.

6. Traditional approaches to flood alleviation can themselves create further

problems elsewhere.

Shaffer et al (2004) list a number of drivers for sustainable water management:

climate change, demographic changes, potential reduction of surface runoff and

urban pollution, potential to save costs and planning requirements such as the

need to comply with Planning Policy Statement (PPS) 25: Development and

Flood Risk (DCLG, 2006a) and the Building Regulations Part H: Drainage and

Waste Disposal (DCLG, 2006b). Roaf (2006) also provides a similar list of

drivers: climate change, demographics, increasing rates of per capita



54

consumption, increasing rates of groundwater extraction, freshwater reserve

depletion, increasing concentrations of chemical and organic pollutants in rivers

and lakes, and increasing public opposition as well as practical barriers to major

new dam projects.

The search for alternatives to the traditional solutions to urban water

management are by no means limited to rainwater harvesting systems. There is

on-going paradigm shift occurring in the UK towards the application of more

sustainable and holistic approaches. Some of these measures include, but are

not limited to:

The use of SUDS for urban drainage (Martin, 2001; Wilson et al, 2004;

Woods-Ballard et al, 2007).

Demand management measures (Butler & Memon, 2006).

Increased metering of domestic properties (Roaf, 2006).

Voluntary codes of practice for improved water efficiency in new homes

(e.g. DCLG, 2006c) and other buildings (e.g. BREEAM, 2007).

Proposed changes to the regulatory framework and Building Regulations

(House of Lords Select Committee, 2006).

Improved leakage management strategies (Trow & Farley, 2006).

Financial incentives such as the Enhanced Capital Allowance (ECA)

scheme for water efficient technologies (HM Revenue & Customs,

2007a)

Research projects (e.g. Balmforth, 2005).



55

Existing legislation that places water companies under a Duty to promote

water conservation to customers, such as the Environment Act 1995

(Roaf, 2006).

New legislation such as the Water Framework Directive (EC, 2000;

Sakellari et al, 2005).

Rainwater harvesting for non-potable uses in urban areas primarily resides in

the „demand management‟ category as the primary objective is to reduce the

volume of mains water used. If RWH systems can reduce reliance on the public

water supply then arguably there is good reason to believe that they can

contribute towards the new sustainable urban water management paradigm.

There are also a range of other potential benefits such as reducing the risk of

urban flooding, financial savings and helping to offset the need to develop

further resources (Leggett et al, 2001a). In some locations the provision of RWH

systems may be a condition for planning agreements (Elliott et al, 2005). One

RWH system supplier stated that about 15% of their domestic sales were

influenced by planning requirements and that this figure would grow

substantially in the future once the Code for Sustainable Homes (DCLG, 2006c)

was transposed into the Building Regulations (Terry Nash of Freerain™,

personal communication, 23rd April 2007). Leggett et al (2001a) provide a

comprehensive summary of the potential benefits of rainwater harvesting and

this is reproduced in table 2.6.



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Table 2.6 Potential benefits of RWH

Adapted from Leggett et al (2001a), pp28-29.

Benefit Stakeholder(s) who benefit Applicability and sensitivity

Reduction in the use of mains water (and potential financial savings)*

Customer in reduced mains water charges Water Supply Undertaker in reduced need for capital investment in water supply infrastructure

Will only have an effect with widespread uptake

Reduced impact on water resources (and potential to offset need to develop further resources)*

Society benefits in an improved natural environment


Reduction in mains supply peak demand

Customer mains supply more assured


Reduction in local flooding risk

Society and building owners

Will only have an effect in a local catchment. This could be significant for new developments

Reduction in stormwater overflow

Society benefits in an improved natural environment Sewerage undertakers in reducing Combined Sewer Overflow (CSO) operation


Development of a new market both in the UK and overseas

Suppliers and manufacturers UK economy

The UK market is likely to develop slowly over the next 10 years (from 2001) but there are clear opportunities in overseas markets such as Germany, South Africa and Australia

Contribution to sustainability

Society, environment, economy

Needs to be reviewed on an individual basis to ensure local sustainability. Sustainability of water resources in the UK will not be affected unless there is widespread uptake

Green public relations Individual organisations, building owners or occupiers

Benefits are being realised even from small projects. This can support corporate or organisational ideals and be used to demonstrate what is possible

Continued on next page



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Table 2.6 continued…

Criteria for development permission

Developers Local Environment Building purchasers

Rainwater on individual development scale enabling development to proceed

Independence from mains water supply

Consumer Requires space and money to meet water needs. Likely to be applied in only a few cases

*Text in italics added by the author

There is a degree of supporting evidence originating from a number of other

countries for some of these benefits, e.g. Schilling & Mantoglou (1999);

Coombes et al (2000a, 2001); Vaes & Berlamont (2001); Coombes & Kuczera

(2003a); Villarreal & Dixon (2005); MJA (2007). However, there are limited

corresponding studies specific to the UK. Some research does exist, such as

that produced by CIRIA and a handful of case studies from the Environment

Agency Water Efficiency Awards, and various university researchers have

published peer-reviewed work. However, there are many claims for the

supposed benefits of RWH that appear to have little substantive evidence to

support them.

For example, Woods-Ballard et al (2007) state that rainwater harvesting has the

advantage of reducing both peak flow rates and discharge volumes, ranking the

performance of both of these indicators as “high” but no evidence or references

are provided with which to corroborate these claims. Similarly, Hassell (2005)

states that “once a rainwater harvesting system is installed, rainwater from the

site is diverted before it adds to the load on the stormwater drainage”. But how

much water can be expected to be retained, and under what circumstances?



58

Again there is no evidence or references provided with which to check this

claim. Some suppliers state that a domestic system can save a typical

household up to 50% of its water needs. However, claims such as these often

appear to be based on an implicit assumption that a system is capable of

meeting all non-potable requirements rather than any empirical analysis which

would indicate that this is achievable in all but a small number of cases, e.g.

Day (2002).

The following sub-sections examine the recognised potential benefits of RWH

systems that are relevant to this thesis. That is, the potential reduction in mains

water use by substituting it for harvested water in non-potable applications. Key

evidence from the literature which is relevant to the UK is highlighted in order to

determine the legitimacy of the claimed benefits that RWH can bring.

Preference was given to studies that included an empirical element rather than

purely theoretical/academic research since the goal was to ascertain actual

measured, not speculative, benefits. Work that merely alluded to potential

benefits and did not provide any supporting evidence or reasoned thinking was

not included.

2.7.4 Reduction in mains water use (and potential financial savings)

A reduction in mains water use is frequently cited in the literature as one of the

primary benefits of installing a RWH system, e.g. see Gould & Nissen-Peterson

(1999); Konig (2001); Leggett et al (2001a,b); Fewkes (2006). For buildings that

contain a water meter, and are therefore charged for mains supply on a

volumetric use basis, there is also the possibility of financial savings since some



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amount of mains water can be replaced by harvested rainwater, resulting in a

reduction in the user‟s water bills. Harvested water should not be considered a

„free‟ resource however as any RWH system has its own associated costs

which have to be balanced against any reduction in mains supply charges.

Whether or not a RWH system can result in an overall financial saving depends

upon a number of site-specific factors, such as RWH system capital, operation

and maintenance costs, local climatic conditions, catchment type and area,

water demand, mains water and sewerage charges and so forth. The

economics of RWH are an important part of this thesis and are covered in more

detail in later chapters. This section in only concerned with reporting the general

results of work done by others in order to assess in broad terms the likely levels

of reduction in mains water use, and whether or not financial savings are

possible.

A small number of UK studies exist in which the amount of mains water

substituted by harvested rainwater was monitored in-situ, with some level of

volumetric water savings observed in each case. The financial benefits were

generally less clear cut, with claims that some systems provided an overall

(often small) financial saving whilst others resulted in an overall financial loss.

For the sake of brevity only the key findings from a selection of cases are

presented here, in tables 2.7-2.9.



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Table 2.7 Key RWH water saving and financial results for the ‘Buildings

That Save Water’ project (Brewer et al, 2001)

RWH system description

Key water saving and financial results

Office building with 50 occupants and 1,500m2 roof area. Indirect RWH system used to supply water to 12 WC‟s and 4 urinals. System included coarse filtration followed by a string filter and a UV unit. Building also incorporated low flush toilets and urinal controls

Annual water usage for WC‟s and urinals was 376m3/yr, of which 150m3 (40%) was supplied by the RWH system. Reduction in annual water bill estimated as £241/yr. RWH system capital costs were £7,250 (purchase and installation). Yearly operating and maintenance costs were £214/yr, yielding a net saving of £27/yr. Payback period estimated as 267 years

Office building/ecological builders merchant located in a newly refurbished 3-storey warehouse with 275m2 roof area. Occupancy was 10 staff, plus visitors. Direct RWH system used to supply 6 WC‟s, 4 urinals and 4 utility sinks used for cleaning purposes

Annual water usage for WC‟s and sinks was 53m3/yr, of which 34m3 (64%) was supplied by the RWH system. Reduction in annual water bill estimated as £40/yr. RWH system capital costs were £3,200 (purchase and installation). Yearly operating and maintenance costs were £27/yr, yielding a net saving of £13/yr. Payback period estimated as 240 years

Ecological housing development consisting of 5 „sustainable‟ terraced houses. All houses self-sufficient in water, no connection to mains supply. Rainwater for non-potable uses collected from roads, an earth banking behind the houses and surrounding grassland was filtered and used to supply water to 5 baths, 10 toilets and 10 taps

Annual non-potable consumption was 377m3/yr, all of which was supplied by the RWH system. Total reduction in annual water bills for all 5 houses estimated as £512/yr (compared to equivalent mains supply). RWH system capital costs were £11,854 (purchase and installation). Yearly operating costs were £110/yr, yielding a net saving of £402/yr. Payback period estimated as 30 years

Notes: financial calculations were basic and did not include the use of a discount rate or irregular maintenance fees such as pump repair/replacement. Inclusion of these factors would have made the systems even less financially efficient. For primary reference, see Brewer et al (2001). See also: Leggett et al (2001a,b).



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Table 2.8 Key RWH water saving and financial results for the

Environment Agency water efficiency awards

Reference RWH system description Key results

Environment Agency, 2001b

Humberstone golf course: existing underground storage chamber adapted for use as part of RWH system for irrigation

Annual water use for irrigation was 4,700m3/yr, of which 1,400m3 (30%) was supplied by the RWH system. Few financial details available, payback estimated at approximately 5 years

Environment Agency, 2003a

Alfred McAlpine sports stadium: water collected from north stand, sports/office complex and selected hard surfaces. Water filtered, UV treated and used for pitch irrigation Great Oak domestic dwelling: 4-bed house with indirect domestic RWH system used to supply WC, basement tap and 2 outside taps Christchurch junior school: indirect system collecting water from 1,100m2 roof used to supply 27 WC‟s, 4 urinals and 2 external taps Denys E Head Ltd: system using a surface pond for storage used to provide irrigation water to garden centre plant nursery.

Annual water savings of 3,119m3/yr reported. No financial details available Annual water savings of 100m3/yr reported. No financial details available Water usage estimated as 876 litres/pupil/yr compared to 3,790 litres/pupil/yr for a similar building, indicating a 77% reduction in water usage. No financial details available Capital costs were £4,000. During first year of operation, system displaced 6,700m3 of mains water, saving over £4,000

Environment Agency, 2005a

Beaumont primary school: rainwater collected from roof and used for WC and urinal flushing as well as garden irrigation Belvedere House: flagship head office of engineering consultancy FaberMaunsell fitted with various water saving devices including a RWH system Sutton Courtenay Environmental Education centre: RWH system for supplying water to low-flush WC‟s to visitors centre with over 5,000 visitors per year

During first year of operation, 170m3 of water was used for aforementioned purposes, of which 63m3 (37%) was supplied from the RWH system. No financial details were available RWH system estimated to have provided 25% of total water use within the building. No financial details available Monitoring showed that RWH system was able to supply 49% of the centres water needs. No financial details were available

Note: no discount rate used in any of the above cases



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Table 2.9 Key water saving and financial results from a number of

domestic RWH system case studies

Reference

RWH system description

Key water saving and financial results

Ratcliffe, 2002

3-bed household in Telford with RWH system supplying water for WC flushing

Water usage for WC flushing estimated at 165 litres/day of which (on average) the RWH system was able to supply 110 litres/day (22% of total household demand). System capital costs were £2,500. No further financial details were available

Day, 2002 RWH system installed at the Millennium Green development, Newark. 24 new homes were fitted with RWH systems for WC flushing, washing machines and outside taps

Results for house on “plot 7”: total water demand over the monitoring period of 248 days was 75.7m3, of which 35.6m3 (47%) was supplied by harvested rainwater. No financial details were available

Stephenson, 2002

Harvesting/irrigation system installed at a garden centre, Gonerby Moor. Runoff collected from 3,000m2 roof area and used to irrigate 15,000m2 plant display area

No figures available but between 2002-2004 mains water only required for relatively brief period after prolonged period of dry weather. Would indicate significant water savings. No financial data available

Fewkes, 1999a

RWH system installed in 2-bed single storey domestic property in Nottingham. Harvested water used to flush two 9-litre WC‟s

Over 12 month monitoring period 63.8m3 was used to flush WC‟s of which 36.4m3 (57%) was harvested rainwater. No financial details were given in this particular paper

2.7.5 Reduction in mains water use: discussion

The evidence presented above illustrates that RWH systems are able to reduce

reliance on the public water supply by substituting mains water with harvested

rainwater for various non-potable end uses, with WC flushing been the most

common. The case studies reviewed indicated that up to ≈50% of non-potable

domestic demand can be met with harvested water but that in practice a wide

range of system performances can be expected. Little data was available with



63

regards to the financial performance and in some cases no financial

assessment was made at all.

Systems installed in commercial and institutional buildings were most commonly

used for WC and urinal flushing. Water saving efficiency varied significantly

between examples and it seems unlikely that generalisations can be made

regarding the performance of such systems. Financially, commercial and

institutional installations would appear to be more viable than the domestic

versions, principally because the former generally have larger roof/catchment

areas and so it is possible to capture a greater volume of water. Also, for a

given commercial/institutional building the level of demand will probably exceed

that found in domestic dwellings, meaning that the potential savings are likely to

be higher for the former building type. However, as with the domestic examples,

limited empirical data was available with which to corroborate these statements.

The application of discounting techniques (in order to take into account the

opportunity cost of capital) was not apparent in any instance, a major limitation

in the those examples that did attempt some form of financial assessment.

2.8 Policy, regulation and guidance

There is currently no formal UK Government policy on the operation of

rainwater systems either in the home or within a commercial/industrial setting.

However, numerous regulations affect system installation as well as use and

some, such as the Health and Safety at Work Act, are relevant even when

installation occurs in a private house. Shaffer et al (2004, pp27-35) provide a



64

summary of a range of policy, regulation and guidance documents that may

apply to the installation and operation of RWH systems. The Water Regulations

Advisory Scheme (WRAS) gives advice on the Water Supply (Water Fittings)

Regulations 1999 in WRAS (1999a,b). Best practice guidance documents are

available from CIRIA as a result of the „Buildings That Save Water‟ project

(Brewer et al, 2001; Leggett et al, 2001a,b). Guidance on the operation and

maintenance of RWH systems as well as example maintenance agreement

documents are provided in Shaffer et al (2004).

2.9 RWH literature review: summary and scope for further work

This literature review has demonstrated that rainwater harvesting is an ancient

technology that has been used around the world for millennia and continues to

be widely used to this day. In developed countries potable RWH systems tend

to be restricted to rural areas. Urban installations are mainly used for non-

potable applications such as WC and urinal flushing, laundry cleaning (washing

machines) and for outdoor uses such as garden irrigation and vehicle washing.

RWH systems have been installed in a wide variety of property types including

domestic, commercial, institutional, public and industrial buildings. The use of

standardised pre-manufactured modular systems is now common practice.

These offer several advantages such as a high degree of design flexibility, ease

of installation, high levels of reliability and a supply of water at a quality

consistently good enough for most non-potable applications.

Regarding water quality, it was noted that many rural communities around the

world rely on harvested rainwater to supply most, if not all, of their domestic



65

water needs including drinking supplies. There have been very few reports of

adverse health effects from drinking rainwater in rural areas. In industrial and

urban areas harvested rainwater often fails to meet drinking quality guidelines,

particularly with respect to microbial standards. However, monitoring studies

have shown that, providing systems are designed and operated correctly,

harvested rainwater usually meets with guidelines applicable to non-potable

uses such as the EU Bathing Water Directive and guidance provided by WHO

and WRAS. The conclusion of researchers in the field has generally been that

rainwater collected from building roofs that has undergone basic treatment

processes (primarily coarse filtration) poses little risk to public health if used for

purposes such as toilet flushing, laundry washing and garden irrigation.

Numerous barriers to the uptake of RWH systems exist. These chiefly relate to

the absence of legally binding water quality standards, lack of high quality

research, current low cost of mains water, water utilities focus on profit

generation and macro scale solutions, unproven benefits, low consumer

awareness, apathy and/or reluctance to conserve water and risk aversion to

new technology. However, despite these obstacles the increasing pressure on

existing water resources, coupled with the apparent unsustainability of the more

traditional supply-side solutions, means that demand management options such

as RWH are likely to play an increasing important role in supplying the UK‟s

future water needs. Currently the UK market for RWH systems is small

compared to some other developed countries but appears to have significant

potential for growth.



66

The potential benefits of RWH systems were identified. These included

reductions in metered mains water use and associated financial savings, as well

as reduced pressure on water resources and reductions in peak demand, local

flood risk and stormwater overflows. However, it needs to be recognised that

many of these benefits remain unproven within a UK context, with only a

reduction in mains water use having any reasonable volume of supporting

empirical evidence. Further work needs to be done in order to determine the

magnitude of the other possible advantages, if indeed they exist at all.

The remainder of this thesis focuses on the potential water saving and financial

benefits of RWH systems for new-build developments, particularly with regards

to the financial performance and viability of domestic installations. The scope of

the investigations was set at the single building scale as this can be considered

to be the basic „unit‟ for RWH system operation. Results generated at this level

could also be used in future studies concerning RWH system implementation at

the development and regional scales, which currently also lack good quality UK-

specific data.

Before any detailed research could be conducted it was first necessary to

determine the state of the art with regards to the design and financial

assessment of contemporary RWH systems. These aspects are examined in

the following two chapters.

uk; rainwater harvesting literature review - bradford university

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