sustainable water management in buildings, an affordable ... · sustainable water management in...

Sustainable water management in

buildings, an affordable approach. Case

Study: Terra Bio-Hotel Project, Medellín,

Colombia

Guillermo Leon Penagos García, Msc Alexander González Castaño, PhD

[Universidad Pontificia Bolivariana de Medellín [Universidad Pontificia Bolivariana de Medellín

PVG Arquitectos SAS] LEET – Laboratorio de Estudios y Experimentación Técnica

en Arquitectura]

ABSTRACT

Water management model in cities is based upon large-scale systems which take water form external

watersheds located dozens to hundred kilometers to the municipalities they supply. Water is treated to

drinking standards despite the intended use, leading to wastewater which is discharged back to the

environment through sewer systems, often without previous treatment, being an important source of

environmental pollution and public health hazards. Meanwhile rainwater is considered a problem, being

collected from roofs and streets to be also disposed in sewers as other kind of wastewater. Although water

technologies have evolved, this model has virtually remained the same since the ancient Rome, twenty

centuries ago. A paradigm shift is urgently required and buildings must be in the center of this

transformation. Terra Bio-hotel, a 41 room hotel located in Medellín is a project designed and being built

with sustainable water systems, integrating low consumption devices, rainwater harvesting, greywater

recycling and groundwater catchment. Although the building is connected to the municipal service,

altogether these strategies allow the project to function as net-zero as for water is concerned. As expected,

the water management scheme of this project is considerably more expensive than a conventional one.

Nevertheless, when operation costs are compared to conventional water fares, it appears that investment

costs are returned in five years, demonstrating eco-efficiency to be an economically sustainable choice at

this scale.

INTRODUCTION

As world urbanization increases so does the pressure upon water resources. This is particularly true

for Latin America and the Caribbean, where 80% of population lives in cities which are dependent on

external water sources to supply, where wastewater treatment is low and vulnerability to urban floods from

storm water is high (Howe, Butterworth, Smouth, Duffy, & Vairavamoorthy, 2012; World Bank, 2013)

This unsustainable condition is related to sectorial water frameworks where local governments,

environmental agencies and water companies work for contrasting agendas and measure their challenges

and achievements by divergent indicators, whereas citizens, private sector and public institutions remain

as passive users, with no say on water governance (Domenech, 2011; Bedoya, 2011)

Since urban water is mainly used and polluted through building operations; water-efficient buildings

are a reasonable starting point to give users a more meaningful role on water governance. This paper

30th INTERNATIONAL PLEA CONFERENCE16-18 December 2014, CEPT University, Ahmedabad

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describes and discusses the water management model implemented on Terra Bio-Hotel Building in

Medellin – Colombia, as a study case, whose comprehensive adoption on other building projects in Latin

America and other regions may make a significant contribution for cities to become less dependent, more

efficient, healthier, less contaminant, more resilient and more sustainable with regards to water (Howe,

Butterworth, Smouth, Duffy, & Vairavamoorthy, 2012).

OBJECTIVE

The aim of this applied research was to conceptualize, develop and implement a model for water

efficiency on a real scale building in Medellín – Colombia and to forecast the expected environmental and

financial cost-benefit ratio in order to provide governs, planners, designers and constructors a framework

to make informed decisions on sustainable water management schemes.

PROCESS APPROACH

Case study

Terra Bio-Hotel is a medium size hotel building with 41 rooms and 2400 m2 built area, looking to be

distinguished for its environmental standards at both construction and operation phases, giving host a

differential factor concerning architecture and technical facilities.The project is set in Medellín, biggest of

ten municipalities assembling a metropolitan area called the Aburrá Valley, inhabited by 3.5 million

people.

Water management data for Aburrá Valley

Information concerning water management for Aburra Valley was collected and analyzed from local

land and water plans, publications by local environmental authorities and local Water Service Company,

as well as from technical relevant literature.

Water management systems for the case of study

Prior to hydraulic design, two water system schemes were pre-designed, analyzed and compared.

System 1 is conventional, whereas System 2 is an alternative system proposed to lower the environmental

impacts related to water demand and wastewater disposal along operation phase of the building (see figure

1).

Figure 1. Water treatment systems installed at Terra Bio Hotel

30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad

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Water treatment plants for System 2

In order to fulfill the principles for System 2, two treatment plants are required: one plant to treat

grey water to be reused on activities that do not require drinking-quality water, such as toilet flushing,

general maintenance and irrigation of green areas; the other plant is to treat rain water and groundwater

up to drinking-quality standards, to be used for showers and faucets. Both rainwater and groundwater were

previously sampled and tested for compliance to water quality regulations set for water sources intended

for domestic supply (data not shown).

Cost-benefit analysis

Financial investment costs for pre-designs of each hydraulic system scheme were calculated. Water

demand is estimated as established for hosting facilities by Colombian regulations.

Environmental costs-benefit analysis is based on the following indicators:

Total water consumption (m3/year)

Dependency on water sources external to the watershed (m3/year)

Wastewater discharge (m3/year)

Storm water discharge (m3/year)

RESULTS

Water in the local context: Water management model in the Aburrá Valley

Table 1 provides main data concerning water management in the Aburrá Valley, which is highly

dependent on external water sources despite of its high water yield. Most urban population has access to

water supply, but unaccounted for water is high. Most population also has access to basic sanitation trough

connection to a sewer network, although the level of wastewater treatment remains low. New wastewater

treatment facilities are under construction and will be fully operating by 2015 though. Due to such

investments, sanitation is charged higher than supply. Groundwater is an abundant source and it is used,

mainly by industry, but total withdraw is unknown. For building sector, such abundance becomes a

problem since parking lots and basements get below the water table, thus water has to be pumped out and

discharged into the sewer system which is charged at sanitation fares, this would also be the case for Terra

Bio Hotel project (see table 1) (Municipio de Medellín, 2014; URBAM, Área Metropolitana del Valle de

Aburrá, & Municipio de Medellín, 2011)

Table 1. Main Data Describing the Current Model for Water Management in the Aburrá Valley

Parameter Value

Water cycle balance

Valley Area (km) 1250

Average precipitation (mm/year) 1672

Average evaporation (mm/year) 1172

Water yield (mm/year) 500

Water yield (million m3/year) 625

Water supply

Total water consumption from water supply (million m3/year) 192

Dependency on external water sources –watersheds located outside Aburrá Valley-

(%) 90

Unaccounted for water (%) 40

Volume extracted from external sources, considering unaccounted for water (million

m3/year) 288

Population served (% of total urban population) 99

Wastewater


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Combined sewer network (%) 60

Sewage currently being treated (%) 20

Water reuse 0

Population served (% of total urban population) 99

Rainwater

Rainwater use (%) 0

Conventional drainage (%) 100

Groundwater

Recharge (million m3/year) 400

Water table depth on the alluvial plain (m) 4 - 8

Groundwater extraction (million m3/year) unknown

Environmental costs comparison

Figures 2 and 3 show a water balance conceptual model for System 1 and 2

System 1 consists of:

100% of water needs supplied by the local water company

drinking-quality water is used for all purposes

no reuse is considered

rainwater is directed to sewer without use

since parking lot base is below water table, groundwater is pumped in order to prevent floods

and discharged into sewer with no prior use

Principles for System 2 are:

water needs supplied from diverse sources

water source defined according to required quality by use

reuse is considered

rainwater as well as groundwater are caught, treated and used

As shown in figures, System 1 produces more environmental impacts than System 2. Water demand

for the two systems is the same, but system 1 requires 40% more water, since it fully depends on external

sources (table 1). System 1 also produces more pollution since groundwater and rainwater are not

harvested but just discharged on sewers and grey water is not reused.

Figure 2. Water balance conceptual model for conventional water management system, System 1.

Numbers are expected volumes expressed as m3/year. Frame fill colors are related to

water quality: white = high quality, black = low quality.


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Figure 3. Water balance conceptual model for alternative water management system, System 2. Numbers are expected volumes expressed as m3/year. Frame fill colors are related to

water quality: white = high quality, black = low quality.

Due to the use of groundwater and rain water as well as the reuse of grey water, implementation of

System 2 not just significantly reduces pollutant discharges from the project but also would eventually

allow it to be fully independent from external water sources (see figure 2), in fact, volume balances for

System 2 shows that the project may produce more water than it actually needs (see table 3)

Cost-benefit analysis

Investment cost

Table 2 lists the investments required for hydraulic installations under Systems 1 and 2 schemes.

Implementation of the efficient water management option costs as much as 38% more than implementation

of the conventional system.

Table 2. Investment cost comparison between System 1 and System 2

Item Cost for

System 1

Cost for

System 2 Description

Water pumps $ 28.947 $ 32.632

On System 2 an additional pumping system for

grey water supply is required, but the pumping

capacity required for drinking water supply gets

reduced

Storage tanks $ 10.526 $ 12.632

On System 2 an additional storage tank is required

for grey water supply, but the storage capacity for

drinking water supply tank gets reduced

Drinking water

network $ 9.944 $ 5.966

Drinking water supply network gets shorten on

System 2, since part of it is replaced by the grey

water supply network

Grey water

supply network $ - $ 6.526 It only applies for System 2

Wastewater

network $ 13.158 $ 11.053

It gets reduced on System 2 since part of it

becomes greywater supply network

Rainwater

network $ 6.642 $ 8.105

Rainwater network becomes longer on System 2 in

order to reach treatment system

Treatment

systems $ - $ 18.421 Only applies to System 2


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Sum $ 69.217 $ 95.334

Difference $ 26.117

Operational costs

Table 3 compares both financial and environmental operation costs for the two systems, water

treatment per cubic meter under System 2 costs just 10% of the fare charged on water supply and 6% of

the fare charged on sanitation. Hence the cost of using rainwater is 10% of conventional supply.

Groundwater use and grey water reuse have a further benefit since these volumes do not get charged for

sanitation. Altogether operational cost for System 2 is 40% of operational cost for System 1, allowing full

return of the additional investment costs by year 3 of operation. On a 30 year lifecycle basis System 2

leaves the project a US $ 261000 net benefit over System 1 (see figure 4).

Table 3. Operation cost comparison between System 1 and System 2

Item Symbol Metric Value

Number of romos R 41

Water demand (m3/room/day)

According to Colombian

regulation

wd 0,5

Occupation index for hotels in

Medellín (%) oi 75%

Daily water demand (m3/day) dd r*wd*oi 15,4

Total water demand (m3/year) WD dd*365 5611,9

Total rainwater (m3/year) RW Average precipitation from table 1 *

On ground building area 534,4

Total groundwater withdraw

(m3/year) GW From case study description 3650,0

Grey water reuse (m3/year) GyW Estimated as 28% of water demand 0,0 1571,3

Dependency on water sources

external to the watershed

(m3/year)

DEW

System 1 = WD/(1-Unaccounted for

water from table 1)

System 2 = WD - GW - RW - GyW

9353,1 -143,8

Total wastewater discharge

(m3/year) WW

System 1 = WD + GW

System 2 = WD - GyW 9261,9 4040,6

Supply water costs (US $/m3) wc

Sytem 1 = supply charges from

table 1

System 2 = by treatment plant

providers

0,86 0,08

Supply anuual costs (US

$/year) SWC WD*wc 4.826 443

Sanitation charge (US $/m3) sch From table 1 1,3

Sanitation annual costs (US

$/year) SnWC

System 1 = (WD+GW)*sch

Sytem 2 = (WD-GyW)*sch 12.040 5.253

Total water system operation

costs (US $/year) WOC SWC + SnWC 16.867 5.696

Difference (11.171)


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Figure 4. Comparison of net present costs for the two systems

In spite of requiring higher investment costs, an alternative ecoefficient water management system

shows to be the best choice in order to reduce both economic and environmental costs for this case of

study. Dependency on external water sources and storm water discharge might get down to zero, as total

water demand and wastewater discharge might reduce down to 45% at a financial present net cost of 53%

as compared to a conventional water management system.

DISCUSSION

Aburrá Valley urban water management is characterized by a high dependency on external water

sources, a high unaccounted for water index, a non-regulated groundwater withdraw, a low level of

wastewater treatment and no policies on storm water discharges, leading to a vulnerable, inefficient,

pollutant system. Most Colombian and Latin-American cities might be described likewise (Howe,

Butterworth, Smouth, Duffy, & Vairavamoorthy, 2012; Domenech, 2011)

These concerns are being addressed from centralized approaches such as upgrading supply systems

and building new wastewater treatment facilities, but the role of end users is not yet being considered a

key issue. This paper shows that buildings, as end water users, would significantly improve the whole

system performance by reducing dependency, inefficiency and pollution, while significantly reducing

operational costs, leaving in fact economic benefits on a lifecycle basis (Penagos, 2007; Bedoya, 2011)

The model described here may be adopted by building projects along the Aburrá Valley, similar

approaches might be analyzed, developed and implemented in other Colombian and Latin-American

Cities, which will continue expanding in coming years under uncertain scenarios concerning incidence of

climate change on water availability, which is already a critical threat to human development in the region.

This study would be also a useful base for governments in order to promote policies and regulations

encouraging sustainable water management for healthier cities (Howe, Butterworth, Smouth, Duffy, &

Vairavamoorthy, 2012; Penagos, 2010)

REFERENCES

Bedoya, M. (2011). AADA - Arquitectura de Alto Desempeño Ambiental: más que una certificación o un

indicador, una metodología conceptual para Iberoamérica. In: Sostenible?, Reciclar Ciutat, Revista

de la Cátedra UNESCO de Sostenibilidad(12). Retrieved june 04, 2014, from

http://cus.upc.edu/publicacions/revista-sostenible/revista-sostenible-1 Domenech, L. (2011). Rethinking water management: From centralizes to decentralized water supply and

sanitation models. Documents d'Anàlisi Geogràfica, 57(2), 293-310.

$ -

$ 100.000

$ 200.000

$ 300.000

$ 400.000

$ 500.000

$ 600.000

0 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Pre

sen

t N

et

Co

st (

US

$)

Year

System 1

System 2

$ 558350

$ 297839


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