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Domestic Water Supply

Engineering Manual


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2

Second edition

Copyright 2000 by

GRUNDFOS A/S

DK-8850 Bjerringbro

Denmark

All r ights reserved.

No part of this book may be reproduced in any form or by any means

without the prior written permission of the publisher.

Drawings: Hakon Lund Jensen

Printed in Denmark


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Domestic Water SupplyChapters

1. Introduction 1

2. Water requirement 2

3. Water sources 3

4. Water quality 4

5. Pollution and infiltration 5

6. Disinfection 6

7. Water treatment 7

8. Pump selection 8

9. Control system andstorage 9

10. Piping and electrical installations 10

11. Trouble-shooting 11


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Contents

IntroductionGeneral 8

Water requirementCalculation of water requirement 12

Water sourcesGeneral 18Drilled wells 19Driven wells 20Washed or jetted wells 21Dug wells 22Bored wells 22Springs 23Cisterns 23

Lakes and rivers 23Capacity check 24Drilled well test 24Diagram for calculating the flow 25Water level measuring 26Procedure 26Regular water level checks 27Driven well test 29Calculation of drawdown at fixed flow 30Spring capacity 31Cistern capacity 32Capacity of catchment area 33Shallow wells 34

Water qualityOfficial tests 36Do-it-yourself tests 36Coliform contamination 37Nitrate contamination 38Consequence of contaminated water 39

Pollution and infiltrationIndustrial and commercial pollution 42Municipal and rural pollution 43Sources of pollution 44Formation sealing of drilled wells 45Sanitary sealing of drilled wells 46Evacuation of gas 47Vacuum wells 47Formation sealing of dug, driven or washed wells 48Formation sealing of driven or washed wells 48Formation sealing of springs 49Design of collecting reservoir 49Other sources of pollution 50

DisinfectionMethods of disinfection 52Chlorination in general 53

Simple chlorination 53Chlorination terms 54Super chlorination 55Well injection 56Pumped dose 57Dosing pump capacity 58Injector chlorination 59General facts about ultra-violet light 60Installation of ultra-violet light 61Safety control 62Pasteurization 64Reverse osmosis in general 65Solar distillation in general 66

Water treatmentWater treatment in general 68Hard water 70Ion exchange in general 72Recharging 73Acid water 74Acid treatment 77Red water (dissolved iron) 78Red water (iron bacteria) 82Brownish-black water (Dissolved manganese) 84Fertilizer-contaminated water (nitrate content) 86What is osmosis? 88

Water smelling like rotten eggs 91Turbid or evil-tasting water 92

Pump selectionTypical pump types for water supply 96Centrifugal principle 97Calculation example 98NPSH 98Pump curves 99Maximum suction lift 100Pump curves 101Cavitation 102Pump applications 103

1. Installation conditions 1042. Water quality 1063. Drives 111Normal water flow 117Likely maximum flow 119Sustained use 120Actual pump head 121Friction loss curves and figures 124Example 125


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Contents

Control systems and storageStorage capacity 1281. Capacity of water source versus peak demand 129

Automatic air control device 132Electric water level control and air compressor 134Reservoir 1362. Optimum economy of the water supply system 1373 & 4. Water supply in case of power failure 138

Piping and electrical installationsPiping 140Importance of stable power supply 142Protective equipment 144Different starting methods 146

Trouble-shootingWater hammer 152Solution 152Pipe corrosion 153Solution 153Sand yielding wells 154Solution 154Pump and pipe corrosion 155Solution 155Service overhaul of simple water supply systems 156Regeneration 157State of the system 158Periodic cleaning and service overhaul 159

Calculation of the constant (C) 161


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1

Introduction

Introduction

Chapter 1


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Introduction Domestic Water Supply

Fig. 1 Different types of domestic water consumptionGeneral

GeneralClean water is the key to a healthy life. Abundant wateris the key to progress and a comfortable life.

Water supply systems should be planned the right wayfor any size of installation - single-family house, hous-ing estate, etc. If not, the result will often be a badinvestment, too high operating costs or even unhealthywater.

In this manual, the term Water Supply Systems coversraw water supply, pump equipment, storage tanks,water treatment equipment, distribution pipes and elec-trical installations.

The manual tells you how to plan safe water suppliesfor a house, a farm, a block of flats, etc.

Groundwater is the main source for private water sup-ply systems. The global amount of groundwater is con-stant, based on the worldss oldest recycling system.The system will function forever unless we humanbeings destroy it.


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Introduction Domestic Water Supply

1

Fig. 2 Watering and irrigation

Water for the agricultural sectorFarms need water for a wide variety of applications.The following are typical examples of water usage.

Increased milk production

Practice has shown that providing water (for milkingcows) by means of automatic drinking bowls, so that thecows can drink whenever they wish, increases the yieldof good cows by approx. 4 per cent over watering twicedaily and approx. 11 per cent compared with wateringonce daily.

Yield stability

To most farmers, the most important advantgage of an

irrigation system is the stability yield that can beobtained, i.e.

1. An optimal constant yield year after year, only influ-enced by the sun, fertilization and wind.

2. Production equalizing advantages - all crops giveoptimum yields when the land is irrigated, and thegrowing season is increased, unlike in non-irrigatedareas where the crops often fail completely.

3. Sandy soil will often yield up to twice as much.

4. Irrigation will often prevent erosion of the land.

Importance of water quality

Development of allergy is an increasing problem inalmost all parts of the world. In certain parts of theworld, the use of DDT is still accepted to fight moscitoesand malaria. In these areas, a content of DDT 42 timeswhat is internationally accepted as the maximum valuehas been measured. This shockingly high figure is notjust the result of polluted drinking water, but also of pol-luted food.

It is, therefore, important, too, that water for irrigationand for watering of livestock is of the best quality.

Coming generations depend on our decisions of apply-

ing clean production methods and consequently cleanproducts.

Plenty to eat, butno water!

If I dont getwater, my growthwill be hampered


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2

Water requirement

Water requirement

Chapter 2


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Water requirement Domestic Water Supply

Fig. 3 Problem solving

Calculation of water requirementThe basis for planning a water supply system dependson water requirements.

First determine the daily water consumption and peakdemand.

Then test the water source to see if it will meet therequirements.

Observations have shown that the water consumptionin a house varies a lot depending on housing standards

and life style.During hot periods, watering the garden increaseswater consumption up to 45 times the normal require-ment.

Evaporation from swimming pools and garden pondsalso requires nearly the same quantity of water persquare metre as lawn sprinkling.


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IrrigationGenerally, the yield depends on the type of crop, thesoil and how it is prepared, the use of fertilizers, irriga-tion methods, rotation of crops, weed and disease con-trol.

The table states the maximum yield of certain cropsgrowing in light soil when treated in the optimum way.

If the yield is lower, irrigation should be considered.

Type of crop Maximum yield

Maize 8,000 kg/ha

Cotton 2,800 kg/ha of seeds and lint,

of which 2,000 kg are fibresWheat 5,000 kg/ha

Barley 5,000 kg/ha

Grass 20,000 kg/ha, i .e. 15,000 feed units

Approximate daily water requirement

ApplicationWater consumption

(litres/day)

Home

For kitchen and laundry use, bathing, sanitary use

and other uses inside the house 400 per person

For replenishment of swimming pool 120

Lawn and gardenFor lawn sprinkling per 100 m2 per sprinkling 2,400 (approx. 24 mm)

For garden sprinkling per 100 m2 per sprinkling 2,400 (approx. 24 mm)

Farming

Dairy cows 80 per head

Calves 30 per head

Beef calves (one year old) 80 per head

Breeding cattle and beef cattle 50 per head

Sheep or goats 10 per head

Horses or mules 50 per head

Swine 20 per head

Sows (nursing) 25 per head

Laying hens 40 per 100 birds

Broilers 25 per 100 birds

Turkeys (1519 weeks) 80 per 100 birds

Sanitation (cleaning of installation and milking room) 2,000 per day

Washdown of floors 50 per 10 m3


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Peak demand

Water storage system

Elevated reservoir.

Min. volume: of daily consumption

Non-elevated reservoir.

Limited reservoir

l/s m3/h l/s m3/h

Single-family house(for all activities inside the house)

0.1 0.36 0.34 1.2

Lawn, garden andreplenishment of swimming pool

0.28 1.0 0.28 1.0

Farming (average)(less than 40 head of cattle or 200 pigs)

0.15 0.54 0.56 2.0

Add to this consumption for domestic use, garden and i rrigat ion

Farming (intensive animal production)(more than 50 head of cattle or 300 pigs)

0.28 1.0 0.56 2.0

Add to this consumption for domestic use, garden and i rrigat ion

Cleaning of installation and milking room 0.07 0.25 0.34 1.0

Washdown of floors 0.07 0.25 0.34 1.0


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2

Fig. 4 Correlation between natural precipitation and requirement for water to crops

The irrigation requirement depends on evaporation(evapo-transpiration) which again depends on the type

and stage of crop (germination, growth, ripening). Withan evaporation of 8 mm per ha. per day, 80 m3 of waterdisappears per ha. per day.

Dependent on the number of working hours availableper day, the required flow rate can be calculated as fol-lows:

By multiplying the above figure by the number of hec-tares to be irrigated, the necessary pump performancecan be found.

In order to calculate water requirements using the tableon page 11, the following example may be useful.

Jan. Febr. March April May June July Aug. Sept. Oct. Nov. Dec.

Naturalprecipitation

Saturation andpercolation

Need forirrigation

Water requirementfor crops

mm

Latitude Water requirement

30 A total of 810 mm per day for approx. 220 days a year




80= 4 m3 per ha. per hour.

20


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Example

Assume you have a small farm consisting of a farm-house, garden, swimming pool, family of four, 30 headof cattle, 40 pigs and 1,000 laying hens.

The table overleaf will give you the water requirement.

Home

4 persons, 400 litres per person 1,600 l/day

600 m2 of garden to be sprinkled (6 x 2,400 litres per 100 m2) 14,400 l/day

20 m2 of swimming pool (2 x 120 litres) 240 l/day

Farm

30 dairy cows, 80 litres each 2,400 l/day

Dairy sanitation 2,000 l/day

40 pigs, 20 litres each 800 l/day

1,000 laying hens, 40 litres per 100 hens 400 l/day

Total maximum water requirement 21,840 l/day

At peak demand when using a pressure tank (see page 12):

Home 1.2 m3/h

Lawn and garden sprinkling, swimming pool maintenance 1.0 m3/h

Animals 2.0 m3/h

Dairy sanitation 1.0 m3/h

Probable maximum peak demand 5.2 m3/h


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3

Water sources

Water sources

Chapter 3


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Water sources Domestic Water Supply

Fig. 5 Well drilling

GeneralIf your present water source supplies ample and cleanwater, even during droughts, it is natural to select this

for the new pumping system, too.If, however, a new water source has to be found, thebest and most reliable one would be ground water, butother water sources can also be used if no suitableground water is available in the area.

Before developing a well, local geological services andlocal well drillers should be contacted for advice.

Different types of water sources:

dri lled wells

driven wells

jetted wells

dug wells

bored wells

springs

cisterns

lakes and r ivers

The above types will be described on the followingpages.


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Fig. 6 Drilled well

Drilled wells

A drilled wel l usually consists of a hole dril led to a depthwhere a water-bearing stratum (aquifer) is reachedand lined with a steel or PVC casing. If the

aquifer supplies ample clean water, a screen sur-rounded by a gravel pack is installed. The pumped

water is filtered by the gravel pack. If there are severalaquifers of limited capacity, a well screen is installed inevery aquifer the casing passes through.

Drilled wells can be developed in soil, gravel or solidrock, as special well-drilling machines are available fordifferent underground formations.

Drilled wells typically range from 4" to 10" in diameterwith depths down to 50 metres, but, if necessary, wellsdown to 700 metres can be developed.

It is advisable to provide a clay or cement seal betweenthe casing and the strata at the top of the borehole toprevent surface water from entering the borehole.

A good, drilled well is an excellent source of water as itis usually unpolluted and provides ample water. If, how-ever, the well is affected by pollutants, it may be neces-sary to drill it deeper in order to get down to strata whichare better protected against infiltration.

Cementgrout

Casing

Gravelpack

Screen

Cone ofdepression

Dynamicwater level

Aquifer

Static water level

Installation pit

Drawdown


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Fig. 7 Driven wells

Driven wellsA driven well usually consists of a well point and ascreen of between 1" and 2" screwed on a galvanizedpipe which is driven into the ground until the screen isbelow the ground water table. Normally, driven wellscannot be used if the water table is more than 8 metresbelow the pump.

The capacity of a driven well is usually limited, often toa maximum 12 m3/h, as it has no gravel pack to pro-tect the well screen against blockage by migrating par-ticles. Therefore, it is often necessary to connect two or

more driven wells to the same pump.

To regenerate a driven well, water should be pumpedback through the screen using a high-velocity water jetto flush blocking particles away from the screen.

Driven wells cannot be constructed in rocky ground.

It is extremely important to seal driven wells by meansof cement grout around the galvanized pipe to preventpolluted surface water from penetrating into the bore-hole.

Drive cap

Well pit

Drive pipe

Screen

Well point

Water table


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Fig. 8 Washed or jetted wells

Washed or jetted wells

A 1"2" washed or jetted well usual ly consists of ascreen with a centre pipe and a ball valve as shownabove. At the same time as the well screen is driveninto the borehole, water is forced down the centre pipeunder high pressure. The water jet will remove thematerial at the lower end of the screen. Such wells canhave a depth of up to 8 metres.

3"4" jetted wells usually consist of a casing with a cen-tre pipe. At the same time as the casing is pressed intothe borehole, the water jet forces the material at thebottom of the borehole to the surface through the clear-ance between casing and centre pipe.

When the casing has been positioned correctly, thecentre pipe is pressed deeper down into the borehole tomake room for the well screen. This is then installed atthe end of the casing. The screen is of the telescopictype with an elastic gasket sealing against the casing.

The outside diameter of a telescopic screen is smallerthan the inside diameter of the casing. Such screensare suitable for telescoping through long strings of cas-ing.

Jetted wells with a diameter of more than 3" can be upto 40 metres deep.

Con-

nectingbranch

Filter

Well point

Ball valve

Centrepipe

Centrepipe

Filter

Casing

Screensetting


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Fig. 9 Dug well (left) and bored well

Dug wellsA dug well is usually cased with concrete pipes or con-crete brick masonry with a diameter of 12 metresextending down below the water table causing water toaccumulate in the well. Most dug wells are less than 20metres deep. The pump equipment is typically installedon two or three steel beams, 34 metres above thewater table.

Bored wellsThe auger used to make bored wells can be hand-

operated, but is usually power-driven. Typical welldiameters range from 6" to 14". Such wells are seldomdeeper than 40 metres. The casing is often made ofconcrete pipes or short steel pipes which are screwedtogether and inserted as the hole is being bored.

Existing wells are often a combination of a dug well anda bored well, as the originally dug wells have dried upbecause of a lowering of the water table by a fewmetres and a hole has been bored down below the newground water table to obtain ample water al l year round.


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3

Fig. 10 Other water sources

SpringsA spring is ground water under pressure which hasbeen forced through the permeable strata to the sur-face of the earth. Springs are rather common in hilly ormountainous areas. Normally, springs give off so littlewater that a reservoir has to be built to ensure a reliablesupply during peak demand.

CisternsA cistern usual ly consists of a watertight underground

concrete tank which is filled with rainwater from roofs.In dry periods, water is drawn into the cistern fromareas with a reliable water supply.

Cisterns are used in areas where no suitable groundwater is available, e.g. islands and peninsulas wherethe ground water is saline. Water from springs or cis-terns should not be used for cooking purposes or asdrinking water if safe ground water is available. Springwater may be subject to some pollution.

Lakes and riversLakes and rivers consist of surface water.

Water for use in the household should never bepumped directly from here to the consumer, but shouldbe taken from a shallow well at the lake shore or riverbank and filtered through at least 510 metres of sand,as it may have been exposed to pollution and pesti-cides.

Spring Lake

Cistern


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Fig. 11 Performance test

Capacity check

When the water source that best meets the require-ments has been selected, the following must be per-formed as a minimum:

Determination of capacity and drawdown

Analysis of water quality (discussed later)

Drilled well test

When a well is drilled, you will normally have a testreport from the well driller.

If you cannot obtain updated information on the capac-ity, the well driller or local pump dealer can probablysupply a test pump. Let it operate for 24 hours, if possi-ble, at a pumping rate corresponding to the calculatedpeak demand and then measure the drawdown. Use awater meter for measuring the flow.

If no water meter is available, fit an undersized pipe tothe outlet of the discharge pipe in horizontal positionand measure the height from ground level to the pipecentre.

During pumping, measure the length from the pipe out-let to the splashing point. With these two values, it ispossible to find the approximate flow from the diagram.

Water

level tapemeasure

Watermeter

Drawdown atpeak demand


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Fig. 12 Measuring of flow without a water meter

Diagram for calculating the flowNote that the discharge pipe must be fully filled with water.

Minimum 1.5 metres

h

x

Xinmetres

Horizontal

X

h

4

3

2.5

2

1.5

10.90.80.70.60.5

0.4

0.3

0.2

0.10.1 0.2 0.3 0.4 0.6 0.8 1.0 1.5 2 2.5 3 5 7 9 Q in m3/h

10mm

1/2"

20mm

25mm

3/4"

1"

11/4"

30mm

40mm11/2"

50mm2"

60mm

21/2"

80mm3"

100mm4"

h in metres

Example:Pipe: 1 1/2"X: 1.2 mh: 1.5 m

The flow rate (Q)is found to be10.7 m3/h

0.1 0.2 0.3 0.4 0.6 0.8 1.0 1.5 2 2.5 3 5 7 9


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Fig. 13 Measuring of water level

Water level measuringWhen the pump performance has been measured, thedepth to the dynamic water level must be measuredtoo. This can easily be done by means of water levelmeasuring equipment, which you may borrow from thewell driller.

ProcedureLower plumb slowly into the well. Make sure that thecable is not damaged by the sharp edge of the upperend of the pipe if not properly deburred. When the built-in electrode is immersed in water, the red light willswitch on. Pull the cable up slightly; when the electrodeis no longer in the water, the light will go out. The exactdistance to the water level can thus be read on thecable.


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Fig. 14 Installation for checking the drawdown

Regular water level checks

For regular checks of the drawdown, it is advisable toinstall a water level indicator together with the pump.

The water level indicator consists of a rigid 1/8" plastictube connected to a pressure gauge and an air valve.

Procedure

1. Fit the open end of the tube to the riser main.Measure the distance from the pump inlet to theopen end of the tube. Install the pumping equip-ment in the well - while measuring the vertical dis-tance from the open end of the tube to the groundlevel. It is important that the open end of the tube isnot fitted closer than 30 centimetres above thepump inlet. One metre is recommended.

2. Record the distance from ground level to the openend of the tube.

3. Pump air into the tube until the pressure gaugereading remains constant. If the pressure gaugepointer returns to zero, there may be a small leak inthe tube connections, or the water level is belowthe open end of the tube. Check for leaks in thetube or at the connections and then fill up with airuntil the pressure gauge pointer remains constant.

4. Record pressure gauge reading.

5. Start the pump.

1 metre


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Fig. 15 Readings and calculations6. Measure the quantity of water.

7. Check the pressure gauge reading at the end of thepumping period, while the pump is still running.

8. Subtract the lower reading from the higher reading.Most pressure gauges are calibrated in bars.In the figure, the difference between the two read-ings is 0.5 bar.

9. Multiply the reading (in bars) by 10. A 10-metre wa-ter column will develop a pressure of one bar.Consequently, the drawdown can be calculated inmetres by multiplying 0.5 bar by 10. The drawdownitself (static water level less dynamic water level)says nothing about the water level above the pump;however, it tells you whether the screen is c loggingor not.

10.Calculation of water level above pump. Multiply thelower reading (0.7 bar) by 10; this gives a dynamicwater level of 7 metres above the open end of thetube. The open end of the tube is one metre abovepump inlet and the total water level above pumpinlet is 8 metres during pumping.

Initial reading

Final reading


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Fig. 16 Testing of driven wells

Driven well testFor small-diameter driven or jetted wells, the pump suc-tion pipe may be the only means to check the drawdownand the friction loss in the suction pipe. Use a jet pumpfor the task. This pump will lift water up to 78 metresunder normal conditions. Fit a non-return valve and avacuum gauge on the suction side of the pump asshown.

Procedure

1. Prime the pump.

2. Start the pump and let it run until the well is free of

air.

3. Stop the pump and check that the vacuum gaugepointer does not move.

4. Record gauge reading (static water level).

5. Restart the pump and throttle the pump until therequired peak demand is obtained.

6. Make sure that the vacuum gauge pointer does notmove. If it vibrates, this might be an indication thatthe pump is cavitating.

7. Record gauge reading (dynamic water level) at theend of the test period.

8. Subtract lower reading from higher reading.The difference is a combination of drawdown andfriction loss.


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Fig. 17 Drawdown

Calculation of drawdown at fixed flow

As the hydraulic condit ions around the screen inlet areunknown, the drawdown can only be roughly estimatedat other flow rates using the following formula:

Drawdown = constant factor flow rate squared.

Known data: Q = 1.4 m3/h at D = 4 metres

At a flow rate of 1 m3

/h, the drawdown D = C Q2

=2.04 12 = 2.04 metres, which is approximately half thedrawdown at a flow rate of 1.4 m3/h.

This calculation may be necessary if the dynamic waterlevel at peak demand drops so much that the pumpstarts cavitating.

In case of cavitation, the only possibility is to throttle theflow on the discharge side of the pump and thus reducethe drawdown.

If the pumpcavitates,throttle theflow rate on thedischarge side Throttle valve

Drawdown:2.04 metres ata flow rate of1 m3/h

Drawdown:4 metres at aflow rate of1.4 m3/h

Dynamic waterlevel at throtledpump flow

Dynamic waterlevel at peakdemand

D = C Q2 C =D

Q2

Constant factor C =Drawdown

=4

= 2.04Flow rate squared 1.42


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Fig. 18 Calculation of spring capacity

Spring capacityAs the amount of water in springs tends to fluctuate

over the year, the flow should be checked in the driestseason. If the spring is on a hillside, the easiest way tocheck the flow is to make a channel with a notch weir.

Fig. 19 Calculation diagram

If this arrangement is not satisfactory, you have to

arrange with your pump dealer for a test pump to checkthe spring.

If you have noticed major variations over the year, thespring is not reliable as a water source. It may also con-stitute a health risk, if not properly protected. Forsprings with a capacity exceeding the daily needs, butstill less than peak demand, a reservoir must be con-structed.

Dug channelDepth of water to thebottom of the notch V-shaped weir

Spring

m3/h

h(cm)

200150100806040302015108654321

90

h

30

20

2

15

108

654

3

1


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Fig. 20 Cistern installation

Cistern capacity

Cisterns should only be used when all other sourcesfail. In practice, some other water source is often usedin combination with a cistern, e.g. water brought in byroad tanker.

To calculate the size of the cistern, the following infor-mation is required:

1. Minimum annual rainfall recorded in the area.

2. Difference between minimum rainfall in the wetseason and the daily consumption that is to bestored for the dry season.

3. The degree of collection in the area (normally, there

is a total loss (e.g. from evaporation) of3040% of the rainfall before it is collected in thecistern).

4. The longest period of drought recorded for thearea.

5. The available roof area from which water can bedrained into a cistern.

Rain-collecting surfaces are called catchment areas.

A catchment area includes both roofs and paved

areas. The latter method is occasionally used in dryregions or on islands and peninsulas with saline groundwater.

Rainwater pipe

Deposits

Pump for removal ofsediments

Filter intake

For supply tank

Screen


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Fig. 21 Catchment area

Capacity of catchment area

In the table, deduction has been made for losses(approx. 1/3) due to evaporation, leakage and removalof tank sediments.

With this information, it is possible to calculate whether

the precipitation is sufficient to satisfy the annual re-quirement

it is possible to build a cistern big enough to store

excess water from the wet season to the dry seasonfor use in the dry season.

Catchment area is based onthese measurements

A = area of roof surfaceB1

B

L1

L3

L4

L2

B2

A B1L1 + L2

2-------------------- B2

L3 + L4

2--------------------+=

Net amount of waterper square metre of catchment area

Minimum annual rainfall[mm]

Annual quantity of water persquare metre

[litres]

100 66

200 133

300 200

400 266

500 333

600 400

700 466

800 533

900 600

1000 666


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Fig. 22 Shallow well test

Shallow wellsLakes and rivers should only be used directly as a watersource for irrigation.

For drinking and cooking purposes, water should betaken from a well constructed close to the river bank.

Check the capacity of the well by means of a watermeter and the drawdown when the pump is thrott led forpeak demand.

If there is space enough, the string-and-float methodcan be used to check the drawdown. In other situations,see page 24.

Dynamic water level

Static water level

Float

Plumb

Drawdown


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4

Water quality

Water quality

Chapter 4


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Water quality Domestic Water Supply

Fig. 23 Laboratory

Official testsWhen the water source has been developed, it is of theutmost importance to have the water quality checked.

You may contact your local health authorities or an

analytical laboratory to have the water tested, both

chemically and bacteriologically. The results of this willshow whether the water source meets the qualityrequirements in your country.

Do-it-yourself testsIf the water source is exposed to pollution, which is thecase for

springs, cisterns, lakes and rivers,

water stored in open containers at temperatures

higher than +15C for more than three days beforetapping,

it is a good idea to test the water regularly. For this pur-pose, a number of do-it-yourself kits are available. Withsuch test kits it is possible to check the occurrence ofthe most frequent types of pollution such as

coliform bacteria from warm-blooded animals orhuman beings.

Nitrate coming from both natural and artificial fer-tilizers.

Changes in pH value.


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Fig. 24 Test for coliform bacteria. Do-it-yourself test kits are available with step-by-step instructions

Coliform contaminationA newly completed well will contain coliform bacteria forat least 50 days.

If the well has had a service overhaul, the same may bethe case.

If coliform bacteria can be detected permanently in thedrinking water, the water source constitutes a healthhazard.

After 48 hours in an incubatorat a temperature of 38C, anycoliform bacteria will have

developed a growth colony

Water containingcoliform bacteria


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Fig. 25 Test for nitrate contamination caused by fertilizers

Nitrate contaminationNitrate in the drinking water may well stem from rainthat fell on a fertilized field some 40 years ago.As nitrate is easier to trace than the various pesticidesthat have replaced each other since the intensificationof agriculture started in the 1960s, nitrate is used as apossible indication of other environmental poisons.

Water containing nitrate


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Fig. 26 Test for pH value. At pH values lower than 6, calcium oxide should be added to the water to avoid corrosion

Consequence of contaminated waterIf the water source contains coliform bacteria or nitratein small quantities, it does not necessarily mean that itis infected with typhoid fever germs, disease-causingbacteria or parasites, but it does tell you that you haveto consider disinfection of the water and that the sourceof pollution should be found and eliminated. If not, anew water source will have to be developed.


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5

Pollution and infiltration

Pollution and infiltration

Chapter 5


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Pollution and infiltration Domestic Water Supply

Fig. 27 Industrial and commercial pollution

Industrial and commercial pollutionContamination of lakes, rivers and underground watersources is often the result of ignorance, carelessnessand a wish for fast profit. Many rivers are so pollutedthat large investments in water treatment are requiredto provide safe drinking water.

Ground water sources which make up 2030 times asmuch water as all lakes, streams and rivers, were onceconsidered protected against contamination by theoverlying layers of earth - but now we know that theyare as likely to be contaminated as surface water if notprotected.

It is only a question of time.

There are two types of ground water contamination:

1. Infiltration of the ground water because of pollutedwater passing the aquifer on its way to a stream or

the sea.

Your chance of stopping contamination is limited to

supporting movements in the region aiming at mini-

mizing the overall pollution.

2. Pollution seeping down at your site.

Stopping pollution at your site is left to you alone.

Leakingundergrundstorage tank

Stream Dump Abandoned well

Surfaceimpound

LeakingsewagesystemSpills and leaks

Water table


43/16443


5Fig. 28 Municipal and rural pollution

Municipal and rural pollution

LandfillAbandoned well

Stream

Septic system

Water tablePotable water source

Pesticides and fertilizers

Source Possible major contaminants

Municipal landfill Heavy metals, chloride, sodium, calcium

Industrial landfill Wide variety of organic and inorganic constituents

Hazardous waste disposal sites Wide variety of inorganic constituents (particularly heavy metals such ashexavalent chromium) and organic compounds (pesticides, solvents,PCBs (polychlorinated biphenyls))

Liquid waste storage ponds (lagoons,leaching ponds, and evaporation basins)

Heavy metals solvents and brines

Septic tanks and leach fie lds Organic compounds (solvents), n itrates, sulphates, sodium andmicrobiological contaminants

Deep-well waste injection Variety of organic and inorganic compounds

Agricultural activi ties Nitrates, herbicides and pestic ides

Wastewater and sludge spread on theground

Heavy metals, organic compounds, inorganic compounds, andmicrobiological contaminants

Infiltration caused by urban runoff Inorganic compounds, heavy metals and petroleum products

Deicing activities(removal of snow and ice on roads)

Chlorides, sodium and calcium

Improperly abandoned wells andexploration holes

Variety of organic, inorganic and microbiological contaminants fromsurface runoff and other contaminated aquifers.


44/16444


Fig. 29 Pollution

Sources of pollutionPollution of the ground water is typically caused by one

or more of the following conditions:

Leaking sewage pipes.

Seepage from cesspool.

Open well casing enabling animals to pollute thecasing or shallow well directly.

Lacking sealing around the casing (annular space)allowing unfiltered surface water to drain directly tothe filter setting.

Oil or chemical spillage seeping down (one litre ofoil can make 10,000 litres of water undrinkable).

Overfertilization of fields.

A well-developed and protected water source may lastfor decades, providing safe drinking water. It is there-fore of great importance that the source is protectedand properly sealed.

Casing

Borehole

Annular space

Contaminationfrom overlyingformations

Aquifer


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5

Fig. 30 Protection of wells

Formation sealing of drilled wells

The borehole diameter of a well is usually larger thanthe casing, which leaves an open space around thecasing. This is known as the annular space; it providesan open pathway for contamination from the surface orfrom aquifers of poor quality intersected by the wellbefore this reaches the desired aquifer.

The annular space must be properly filled with grout toprotect the aquifer. The grout consists of cement andwater (usually mixed in the proportion of 50 kg of Port-land cement to 25 litres of water) plus bentonite (specialclay) and additives to reduce shrinkage. A reinforcedconcrete slab at the top of the well is also important forprotection.

Splashproof cover

Frost line

Concrete

Casing

Grout seal

Concrete slab

Concrete slab

Screen sealing

Clay

Filter gravel

Splashproof cover

Well screen


46/16446


Fig. 31 Sanitary sealing

Sanitary sealing of drilled wells

The top of the casing must extend approximately0.3 metre above the surface of the ground or floor andbe watertight with a tight sanitary well seal where thepump connections enter the well. The seal must closeall openings for riser mains, cables and monitoringequipment. If a deep well turbine pump is used, the topmust be sealed by the pump head.

Any vent pipe should be screened to prevent entry ofinsects, snakes or the like.

The ground level around the well top must be con-structed so that it slopes down from the well in all direc-tions.

If the water source is a combination well (a dug wellwhich has been drilled deeper to get down to reliablewater-bearing strata), a drainage pump should beinstalled in the shallow well to drain this during the wetseason when there is an inflow of surface water.

Discharge pipe

Pipe plug

Casing

Submersibledrop cable

Sanitarywell seal

Well vent

Riser main

Rubber

Riser main

Soft rubberexpandinggasket

Well casing


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5

Fig. 32 Evacuation of gas

Evacuation of gasSome wells contain so much gas suspended in thewater that it causes a bad odour or taste. In extremecases, the gas may even block the pump. This can usu-ally be overcome by installing a sleeve around thepump just below the pump inlet, extending upwards asfar as possible.

Vacuum wellsIf the water in the well contains so much gas in suspen-sion that a sleeve is insufficient to meet the water qual-ity requirements, a vacuum must be created in the wellcasing. This can be done by connecting a vacuumpump to the vent pipe when the casing is hermeticallysealed. Before doing this, it must be checked that thewell casing is strong enough to withstand the vacuum.

Gas

GasGround water level

Non-returnvalve

Vacuum pump

Vacuum gauge

Vacuum switch

Gas vacuum

Casing water level

57 m

Gassleeve

Pumpintake


48/16448


Fig. 33 Formation sealing

Formation sealing of dug, driven or

washed wellsThe hole diameter of the dug well is only a little largerthan the precast concrete pipes and the annular spacearound the lower pipes is filled with cave-ins. Pour low-viscosity cement grout around the pipes up to the frost-proof depth. When the cement grout reaches the waterlevel, it will create a formation seal (cake). Between thefrost-proof depth and the concrete slab, plastic clay(bentonite) should be compressed. Clay is only slightlyaffected by frost.

Formation sealing of driven or

washed wellsAs the well point is being driven or washed through theformations, these will be somewhat damaged. This canbe avoided by pouring a low-viscosity cement groutalong the pipe to create a sealing cake at the water

level. Plastic clay should be filled in and compressedfrom the frost protection line to the well slab.

Concrete slab

Splashproofcover

Cementgrout

Clay

Well pointCrushed rock

Water table

Cement grout

Thin cementgrout

Gaskets

Clay

Frost line

Splashproof cover

Ventilation

Gaskets


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5

Fig. 34 Sealing

Formation sealing of springsSprings with a water quality suitable for drinking arenormally located on a hillside. The spring water is col-lected by placing perforated drains wound with fibres inthe aquifer. After installing these pipes, the aquifershould be enclosed in fat compressed clay so that pol-luting surface water will not infiltrate. When construct-ing the collecting reservoir, all surfaces in connectionwith the surrounding clay should be sealed with cementgrout.

Design of collecting reservoirIt is important that a splashproof removable cover isbuilt approximatelly 30 cm above the top of the collect-ing reservoir so that a drainage pump, type KP, can belowered to the bottom to remove penetrating fine sandand silt. It is important to install an overflow pipe withtrap to allow throughflow of the total yield of the springwhen there is no consumption. The trap is designed toprevent mosquito larvae, etc. from hatching in the col-lecting reservoir. A low level cut-out switch should befitted in the collecting reservoir and a ditch should bedug around the source of the spring to carry surface

water round the collecting arrangement.If the spring is in an area with livestock, a fence shouldbe erected at a distance of at least 20 metres from thespring.

Fence

Pump

Overflow

Spring (water-bearing gravel

Perforated pipes

Collecting chamber

Clay and cement grout

Removable cover

Level switch

Perforated pipes

Surface water diversion

Trap


50/16450


Fig. 35 Contamination of well water

Other sources of pollutionIf the water source is safely protected against surfacecontamination as described formerly and still suppliespolluted water, there are two possible polluting sourcesleft:

1. The ground water is infiltrated by contaminatedground water.

2. The water source is contaminated by a dunghill or aseptic tank.

In both cases, it is too late to do anything; a new watersource has to be developed somewhere else. Geologi-cal conditions determine where the most reliable

water source can be found. Often you have to searchfurther upstream.

Septic tank

Underground disposal system


51/16451


6

Disinfection

Disinfection

Chapter 6


52/16452

Disinfection Domestic Water Supply

Fig. 36 Different weapons against bacteria

Methods of disinfection

If it is not possible to find a non-contaminated watersource, the water must be disinfected for human andlivestock use. There are five different methods tochoose between:

1. Chlorination

2. Exposure to ultra-violet light

3. Pasteurization

4. Reverse osmosis

5. Solar distillation (only in tropical regions)

Ultra-violet light

GermsChlorine

Contaminatedwater

Germ exit

Waste

Purifiedwater

Reverse osmosis (screening)

Screen

Pasteurization


53/16453


6

Chlorination in generalChlorination is the most common method of disinfectiondue to its lasting effect after the initial dose. This means

that germs will be eliminated in stagnant water pipes.The other disinfecting methods will only kill bacteriaand viruses as the water passes through the disinfec-tion zone. If a virus or bacterium is allowed to infect thewater after the disinfection zone, it will breed uninhib-ited.

The chlorine method has two minor disadvantages:

1. Chlorine in water leaves a slightly unpleasant tastein the mouth; coffee and tea taste different whenmade from chlorinated water.

2. If chlorine is applied in too large a quantity, it will

have a corrosive effect on most metals andelastomers.

Simple chlorinationThe quantity of chlorine to be added in order to disinfectthe water depends on the composition and temperature

of the water as well as on the retention time (the timepassed from when the chlorine is added till water con-taining chlorine comes out of the tap). The typical dos-age is 1.01.5 mg/litre at a retention time of approx. 30minutes.

The quantity of chlorine must be increased if

the retention time is shorter than 30 minutes

the amount of iron, sulphur, ammonia or organicmatter is substantial

the water temperature is below 10C

the pH value of the water is higher than 7


54/16454


Fig. 37 Enemies of chlorine

Chlorination terms

Only little chlorine is needed to kill bacteria whereas alittle larger amount is necessary to kill viruses. The dos-age is measured in mg/litre or part per million (ppm).1 ppm is equal to one litre of concentrated chlorine inone million litres of water or one litre of concentratedchlorine in 1,000 m of water.

Some of the added chlorine is passivated by the metals,minerals, slime and organic matter in the water and isconsequently made inert. Some of the added chlorinewill combine with the ammonia present in the water,which will hamper the killing action. This is called com-bined chlorine residual. The remaining chlorine is

called free chlorine residual.

The free chlorine residual is approximately 20 timesmore effective in destroying bacteria than the combinedchlorine residual, so it is the free chlorine residual youmust rely on and check.

The free chlorine residual content must periodically bechecked. Usually a test kit is supplied with the chlorin-ator unit. If not, it can be purchased separately.

The free chlorine residual must be at least 0.20.5 ppmafter 30 minutes retention time in water with a pH valueof max. 7.

If the pH value is higher than 7, the chlorine residualmust be at least 0.8 ppm.

Chlorine dosage

Ammonia

Minerals

Chlorine demandCombinedchlorine

residual

Chlorine residual

Metal

Slime and organic matter


55/16455


6

Fig. 38 Simple chlorination and super chlorination

Super chlorination

In systems where you cannot ensure 30 minutes reten-tion, a larger quantity of chlorine must be used; this iscalled super chlorination.

If the chlorine taste in super-chlorinated water is toodominant for drinking purposes, the taste can beremoved by passing the water through activated car-bon.

Fig. 39 Relation between retention time and residual

chlorine concentration

Systems with short retention time,e.g. where there is low pressuretank capacity

Systems with longretention time, e.g.where there is largepressure tank capacityor chlorination directlyin well

Simple chlorination

(small dosage)

Super chlorination

(big dosage)

ppm

min.302010

0

1

3

4

5

6

5

pH valueabove 8

pH valuebelow 7

Freechlorineresiduals

Retention time


56/16456


Fig. 40 Feeding of tablets containing chlorine

Well injection

In order to prolong the retention time and in this wayreduce the dosage of chlorine, it is practical to injectchlorine directly into the well.

Calcium hypochlorite is available in tablet form. It con-tains approx. 50% active chlorine by weight and can beinjected directly into the well by means of a chlorine tab-let dispenser that only feeds the well when the waterpump is in operation. This method is preferable in areaswhere it is legal to chlorinate directly into the groundwater well. The tablets must be led directly into thewater through a plastic tube to avoid corrosive attackson casing and riser main.

If the well water is infected by iron bacteria which pro-duce iron slime on the screen and the surroundinggravel to a degree that makes the screen clog, the onlyway to keep the well clean is to chlorinate directly intothe well. In this way the iron bacteria will be killed.

Tablets

Well

Tabletdispenser

Tablets

Tube


57/16457


6

Fig. 41 Dosing pump

Pumped dose

If you are not allowed to inject chlorine into the well, itis also possible to chlorinate after the ground water hasbeen pumped up. Sodium hypochlorite is a solution ofsodium, water and chlorine.

Domestic sodium hypochlorite is a 5%chlorine solution

Commercial sodium hypochlorite is a 20%chlorine solution

For dosing, use a membrane pump or the like as itdelivers a definite amount of chlorine solution with eachstroke. The pumping action is usually developed by amembrane and valves that open and close the suction

and delivery of the pump housing.

Principle of

dosage pump

Delivery

Suction

Dosagepump

Plastictubing

Non-returnvalve

Well seal

Sodiumhypochlorite


58/16458


Fig. 42 Dosing

Dosing pump capacityThe pump capacity is adjusted by varying the length of

the pump stroke. The chlorinator pump operates contin-uously while the water pump is in operation.

For a home with a daily water consumption of 2,000litres, the consumption of chlorine at a dose of 10 ppmwill be

When using a 5% chlorine solution, the chlorinator

pump is to pump

which should be dosed when the water pump is in oper-ation.

If it is not possible to find a membrane pump yieldingthe small amount of chlorine needed, it is possible todilute it 10 times with soft water (1:10) and dose a 10times larger quantity.

10 x 2,000= 0.02 litre = 20 millilitres/day

1,000,000

20 x 100= 4 millilitres/day

5


59/16459


6

Fig. 43 Injector chlorination

Injector chlorination

The cheapest form of injector chlorination is achievedby using a jet pump or a centrifugal pump located abovethe ground level. The injecting effect is created by thedifferential pressure between suction side and dis-charge side of the pump during operation.

As water from the discharge side of the pump passesthrough the nozzle at a very high velocity, a suctioneffect is created in the chlorine solution line. Chlorine isdrawn up and mixed with water in the jet stream of thediffusor. From the diffusor, water-mixed chlorine isdrawn to the water pump suction line and delivered tothe pressure tank. The amount of chlorine sucked from

the chlorine container is adjusted by a needle valveplaced in the chlorine solution piping.

This piping must be equipped with a plast ic or stainlesssteel non-return valve to avoid backflow when the waterpump is not operating. In systems where the chlorina-tion process takes place near to the consumer taps, itis important that the volume (in litres) of the pressuretank is half the pumped peak demand per hour in orderto create enough retention time to have the bacteriakilled when using simple chlorination.

If this not possible, superchlorination must be applied.The pressure tank must be equipped with an inlet andoutlet diffusor to prevent water from streaming straightthrough the water tank.

OpenClosed

Sodiumhypo-

chlorite

Test cock


60/16460


Fig. 44 Treatment by means of ultra-violet light

General facts about ultra-violet light

The use of ultra-violet light for disinfection of smallquantities of water for domestic water supply is rela-tively new. However, it is a well-known method for largewater supply systems for which it has been used fordecades.

The method consists in passing a thin layer of wateralong a lamp that emits bacteria-killing ultra-violet light.The ultra-violet lamp is protected against cooling andwater by a quartz sleeve. In this way the lamp can bereplaced without emptying the system of water. Thequartz sleeve tends to become coated with particlesthat limit the emission of light from the ultra-violet lamp.

Consequently, all makes of lamps are available withwipers that can keep the sleeve clean either manuallyor automatically by means of a time control.

Each individual ultra-violet unit is designed for a certainmaximum capacity which must not be exceeded. Con-sequently, most units are available with a flow-regulat-ing valve that throttles the water flow from the pumpwhen too much water is used.

Waterinlet

Outersleeve

Quartzsleeve

Ultra-violetlamp

Wateroutlet


61/16461


6

Fig. 45 Installation with ultra-violet light

Installation of ultra-violet light

The ultra-violet unit should be installed between pumpand pressure tank. The capacity of the unit can beadjusted to the capacity of the pump. When the waterrequirement is greater than the capacity of the ultra-vio-let unit, water will be drawn from the pressure tank.

Example

Max. capacity of ultra-violet unit is 1.5 m3/h.

Water peak demand 2.0 m3 (for short periods).

Total pressure tank volume is 1.0 m3 of which normally2/3 is water, i.e. 0.66 m3 under a pressure of 2 bar.

When too much water is used, the pressure in the mainwill decrease. The compressed air in the pressure tankwill therefore start forcing the water out of the tank intothe pipe system

When the pressure in the tank has dropped to 0.5 bar,the water volume will have decreased to 1/4 of the vol-ume of the pressure tank. A total of 0.4 m3 of water hasbeen forced out of the pressure tank to the taps.

With a pressure tank of 1 m3 we have been capable ofmanaging a peak demand which is

higher than the max. capacity of the ultra-violet unit forapprox. 50 minutes.

Control panel

Watervolume

Airvolume

Absolutepressure(bars)

Drainingvolume

Bars

Manometric

pressure

Tank volume

Flowregulatingvalve

80

70

60

50

40

30

2/3

20

10

0.5

90

%

100

0

1/3 3

1/4 3/4 1.5

2.0

1.0

2.0 - 1.5x 100 = 33%

1.5

0.4 m3= 0.8 h ~48 minutes.

0.5 m3/h


62/16462


Fig. 46 Safety control

Safety control

The intensity of radiation from the ultra-violet lampdecreases over time and it will finally become so weakthat it will no longer kill bacteria and viruses. In order toensure disinfecting efficiency, most ultra-violet unitsare provided with an electric eye. This electric eye reg-isters the light intensity of the most effective radiationfrequency, approx. 2,537 ngstrm. When the lampgets older or if dirt collects on the quartz sleeve, theelectric eye will close the solenoid valve by switchingoff the current for the magnet coil. Consequently, thewater supply will be stopped in case of power failure.

Ultra-violet units are designed for continuous operation.When there is no consumption, the water around thequartz sleeve will therefore be heated. If the water con-tains polluting particles, these will settle around thequartz sleeve. To avoid this, polluted water shouldalways be filtered efficiently before passing the ultra-violet unit.

Light sensor

Solenoidvalve (open)

Flow regulating valve

Safety control


63/16463


6

Fig. 47 Safety control

Safety control

(continued)Another type of safety control on the market measuresthe volt and amp consumption in order to determine thecondition of the ultra-violet unit. An ultra-violet lampreceiving lower voltage than what it has been designedfor will not kill bacteria and viruses as it was designedto do. If this situation arises, the water supply should bedisconnected. This is done by means of a relay whichdisconnects the power supply for the solenoid valvewhen it registers undervoltage in the mains. When thesolenoid valve coil is made currentless, the valve willclose and thus prevent water from passing through.

As the lamp gets older, the l ight intensity decreasesand at the same time the amps consumption increases.This is utilized to activate a current relay. When the cur-rent relay registers power consumption exceeding whatis optimal for the lamp type in question, the relay inter-rupts the power supply for the solenoid valve.

Power supply

Control circuitSolenoid valve

Control circuit

VoltsAlarm

AmpsAlarm

Flow regulating valve

Power supply


64/16464


Fig. 48 Pasteurization

Pasteurization

In areas with hard water and where electricity prices arevery low, pasteurization can be found as a method ofdisinfection. The method is based on the principle thatheating of water to a temperature of at least 70C willkill all bacteria and virus cultures harmful to the humanorganism. At the same time, large amounts of the cal-cium in the water will end up on the heating elementswhich heat the water. This calcium is removed by scal-ing these with acid. To save energy, some of the heatis recovered by sending the heated water through aheat exchanger of the counterflow type where it trans-fers some of its energy to the cold water from the watersource.

The system works in the following way:The cold water (10C) is fed into a heat exchangerwhere it is heated to approx. 68C by the hot disinfectedwater (approx. 75C) which flows through theexchanger in the opposite direction towards the storagetank. From the heat exchanger the water continues to awater heater where it is heated to approx. 75C. Whenit has the right temperature, it is pumped through asolenoid valve via the heat exchanger to the storagetank. If the water does not have the necessary temper-ature, the thermostat controlling the solenoid valve willchange the position of this so that the water is pumpedthrough the heater once more.

75C

68C73C

15C

10C

Storage tank

Con- sumptionTemperature sensor


65/16465


6

Fig. 49 Reverse osmosis unit

Reverse osmosis in generalReverse osmosis is used for disinfection in domesticsystems. However, due to the

higher energy costs in comparison with chlorinationand

removal of taste-creating minerals and salts dis-solved in the water,

reverse osmosis is only chosen for disinfection whenthere is also a wish to remove other dissolved materi-als, e.g. nitrates, chlorides, etc.

Disinfection by means of reverse osmosis is describedin the following chapter.


66/16466


Fig. 50 Solar distillation unit

Solar distillation in general

Distilled water does not taste good, actually it has notaste. Distilled water should always be treated beforedrinking. In some areas, the water is so unfit for drinkingthat treatment by means of reverse osmosis or distilla-tion is necessary. Distillation of water is only competi-tive in comparison with reverse osmosis if solardistillation or distillat ion by means of waste heat can beused.

Solar distillation takes place by concentrating the raysof the sun by using reflectors. If these are designed cor-rectly, the temperature in the focal axis can becomevery high. Here, the water that you wish to distill is cir-

culated at a pressure slightly above atmospheric. Whenthe temperature of the water is approx. 100C, a valvewhich is protected by a thermostat opens. When pass-ing through the valve, some of the water is transformedinto steam. The steam is collected in a pipe whichslopes down to a condensate tank with cooled water.

Concurrently with the evaporation of water from thesystem, new cold water is added so that the processmay continue as long as the solar energy can raise thewater temperature higher than 100C. Impurities con-centrated at the bottom of the tank should frequently beremoved. The water is circulated by a circulator pumpwhich is protected against steam backflow by means ofa non-return valve. It must not be possible to cut off thepipe system completely; there should always be a smallbypass.

Steam and condensate on its way to the condensate tank

By-pass

Thermostatically regulated valve opens at 100C

Circulator

Coldwaterinlet


67/16467


7

Water treatment

Water treatment

Chapter 7


68/16468

Water treatment Domestic Water Supply

Fig. 51 Sources of pollution

Water treatment in generalEven when the water source supplies ample non-infected water, water treatment should still be consid-ered in certain areas to ensure good water quality.

Rain absorbs impurities from the air. Nitrogen is one ofthe gases that after a period of time may cause wells tobe abandoned due to contamination.

Gases like sulphur dioxide (SO2) and carbon dioxide(CO2) react with water to form acids (sulphuric acid andcarbonic acid). These acids will not only kill the forests,woodlands, etc. nearest to the major source of contam-ination. They will also cause chemical changes inunderground strata and consequently affect groundwater quality.

Raincontainingimpurities

Spring

Dump

Gravel

Clay

Ochre

Silt

Sand

Carbon dioxide

Waste water

Swamp

Lake


69/16469


7

When ground water containing sulphuric and carbonicacids seeps through sand, soil or rocks, it dissolveslarge quantities of calcium, iron, aluminium, magne-sium and other minerals, and holds them in a solution.

When this happens, the underground water becomesacid and the chemical reactions as well as the waterquality change.

The water source may be affected so much that thequality of the water has to be improved by treatment.

Various causes for treatment:

1. Hard water (see page 68)(dissolved calcium and magnesium)

2. Acid water (see page 72)(dissolved sulphur and carbon dioxide)

3. Red water (see page 76) (dissolved iron)

4. Brownish-black water (see page 82)(dissolved manganese)

5. Fertilizer-contaminated water (see page 84)(dissolved nitrate)

6. Rotten egg water (see page89)(dissolved hydrogen sulphide gas)

7. Turbid or evil-tasting water (see page 90)(dissolved sediments and organic matter,minerals in high concentrations)


70/16470


Fig. 52 Result of hard water

Hard water

Symptoms

Large quantities of soap are required to get a properresult from washing machines.

The use of soap results in slimy scum and not abright foam.

Glassware and windows appear streaky grey afterwashing.

Heavy coatings below the waterline in the bathtub.

Hot water installations develop hard deposits onpipe walls.

Causes

Calcium and magnesium in the water.

Bicarbonates, sulphates or chlorides in the water.

Dissolved iron in small quantities.

Dissolved aluminium.

Overdose of soap

Grey coatings

Streaky grey


71/16471


7

Fig. 53 Result of hard water

Hard water(continued)

The hardness of water is mainly due to the calcium con-tent, but many other minerals are absorbed as thewater seeps through the ground.

Hard water normally occurs where the ground consistsof clay, rock or limestone formations.

It is usually only the levels 4 to 5 which cause directproblems. At level 3 it is economic to soften water forwashing machines and dishwashers. For this purpose,lots of chemicals and dosing devices are available.

Very hard and extremely hard water is usually softenedby means of reverse osmosis or ion exchange. Reverseosmosis is described in detail under Fertilizer-contami-nated water (page 84) as it is a universal method oftreatment to remove all undesirable particles fromdrinking water.

Here only ion exchange is described. It is to beobserved that ion exchange of drinking water is not per-mitted in all areas. Therefore the local water authoritiesshould be contacted before installing such a system.

Magnetic flux density:Minimum6,0007,000 gauss

Magnetic treatment ofhard water reducescalcium deposits

Level Hardness of water Concentration

[ppm]

1 soft 50

2 moderately hard 50100

3 hard 1002004 very hard 200300

5 extremely hard >300


72/16472


Fig. 54 Ion exchange

Ion exchange in general

Softening of water by means of ion-exchange is a proc-ess in which some electriclly charged particles (ions)that do not contribute to the hardness of the water, e.g.sodium ions (Na+), are added to a porous material(called an ion-exchange resin).

When sodium chloride (NaCl) is dissolved in water, thesodium atoms (Na) separate from the chloride intosodium ions (Na+) and the chloride atoms (Cl) separateinto chloride ions (Cl).

The sodium ions (Na+) that are added to the ion-exchange resin are lower electrically charged than the

molecules causing hardness, such as calcium ions(Ca++) and magnesium ions (Mg++) in the water.

When passing through the ion-exchange unit, most ofthe dissolved Ca++ and Mg++ ions are replaced by Na+ions. This means that for every exchanged Ca++ ionand Mg++ ion two Na+ ions are received. Na+ ions donot contribute to the hardness of the water. This willresult in softer water.

When most of the Na+ ions have been replaced by Ca++and Mg++ ions, the unit has to be recharged in order tomake the softening process continue.

Section of theperiodic system

Two-tank system

Increasing electric charge


73/16473


7

Fig. 55 Recharging

Recharging

Recharging is carried out manually (the one-tank typeor the resin-replacement type) or automatically (thetwo-tank type), depending on the type of unit. A con-centrated brine solution (NaCl) is passed through theunit, and the Ca++ and Mg++ ions are released andexchanged for the Na+ ions from the salt when passingthrough the ion-exchange resin. When excess salt hasbeen washed out of the exchange material, the watersoftening system functions as well as a new one. As thefrequency of recharging depends on the type of equip-ment, the instruction manual must be consulted.

If recharging is not carried out regularly, bacteria, slimeand dirt may collect on the exchange resin. That is whythe ion-exchange method is not permitted for drinkingwater in some areas.

Persons suffering from a heart disease or circulatorydisturbances should never consume water containingsodium.

Water containing oxidated iron (rust) should be filteredbefore passing through the water softener or a type ofsoftener should be used where used exchange resin isremoved from the container and replaced by a new one.

The old one can then be returned to be recharged.

Section of the

periodic system One-tank system

Increasing electric charge


74/16474


Fig. 56 Results of acid water

Acid water

Symptoms Corrosion on steel parts and copper solderings.

Grout joints in the shower disappear.

Corrosion of steel makes red stains in the washbasin and lavatory.

Corrosion of copper and brass makes green stainsin wash basins and baths.

The iron-removal system does not work optimally.

Causes The water contains sulphuric, carbonic and nitric ac-

ids that have never been neutralized.

Acid may also derive from decaying organic matterfrom swamps or bogs.

Corrosion of brassgives green stains

Grout jointsdisappear

Corrosion on steelpipes and fittings

Corrosionon coppersolderings


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Fig. 57 Results of acid water

Acid water(continued)

Acid water is mainly caused by atmospheric pol lution.Polluted rainwater seeps through the ground withoutpassing through neutralizing substances. That meansthat slightly acid water (pH > 5.5) occurs in places withlime-deficient, sandy subsoils where the topsoil is thinand lime-deficient, and often in places where theground water level is close to the surface. Extremelyacid water (pH < 5.5) occurs in lakes, meadows, andbogs where the amount of water running in is far biggerthan the amount running out. Due to evaporation, theadded acids and acid residue are concentrated - so-called brackish water.

Cold acid ground water is comparatively harmless, butwhen it is heated, it becomes aggressive. The aggres-siveness doubles for every 15C increase. That is whycoffee and tea made from acid water will quickly dam-age your teeth. Likewise, a steam iron filled with acidwater will quickly corrode inside. Drinking water with apH value of 5.56 used for cooking, coffee and teashould be neutralized. On the next page, the acidity ofvarious refreshing drinks, foodstuffs and cleaningagents are compared.

In cold drinks

No danger

Steam irons filled

with acidic water willcorrode inside

Will damage your teeth

In hot drinks


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Fig. 58 Comparison of pH values of different products

pH

1

2

3

5

4

6

7

8

11

12

10

9

14

13

Wine

Vinegar

Gastric juice

Grapes

Orange juice

Lemon

Lime

Potable

water

WineMothers milk

Potatoes

Cows milk

Domestic detergents(medium concentration)

Beer

Domestic detergents(high concentration)

Cider

Tomatoes

Increasingalkalinity

Increasingacidity

Neutral


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Fig. 59Acid treatment installation

Acid treatment

When it has been decided to treat acid water, there areat least three ways to do it:

Neutralization tank (the water passes through lime-stone or marble).

Addition of soda ash.

Addition of caustic soda.

Neutralizing tanks should mainly be chosen for waterwith pH values higher than 5.5 (slightly acid water).

The neutralization tank is filled with limestone or marblechips. The acid in the water reacts wi th (consumes) thelimestone which means that the limestone has to bereplaced frequently. Another way is to purchase a neu-tralization unit where a new bag is simply inserted whenthe old one is used up.

Soda ash is put into chlorine tanks, and in this way thechlorinator is used for neutralization, too.

Soda ash adds sodium bicarbonate to the water. If thisis not acceptable, caustic soda can be used instead.Caustic soda is also called household lye, and itrequires more care in handling than soda ash.

If there is no chlorination unit, feeding has to take placedirect into the well by means of a dosing pump in orderto protect screen, casing and piping against corrosion.

Soda ash

Soda ash

Dosingpump

Non-returnvalve

Aircompressor


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Fig. 60 Results of dissolved iron

Red water (dissolved iron)

Symptoms

White clothes turn reddish or yellow when washed.

Bathtubs and toilet bowls get red stains.

Pots turn red inside.

After a long period without water consumption, thefirst water that comes out of the tap is red.

In extreme cases, the water will taste metallic.

Causes

Corrosion of steel pipes and tanks.

Dissolving action of water as it passes through de-posits of iron in the ground.

Acid ions in the water, even at normal pH values.

The red colour is mainly due to the iron content in thewater. Red-brownish water is the result of iron and a lit-tle manganese in the water. Normally, the oxygen ofrainwater is used up by biological and chemical proc-esses when passing through the ground. That is whyground water is deficient in oxygen, and the iron ionstaken up will not become visible until they are oxidizedinto ferric oxide. In wells where the air above the watersurface liberates oxygen to the water, iron ions getaccess to oxygen.

Metallictaste

Red stains

Iron mouldon laundry

Red deposits


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Fig. 61 Membrane tanks prevent contact between air and water

Red water(continued)

The iron ions will also be in contact with oxygen in thepressure tank in which there is an air cushion at the top,exerting pressure on the water surface.

At a moderate iron content of 0.31.5 ppm in the groundwater, the water quality can be considerably improvedin the following ways:

1. The top of the well is sealed (the access of air to thewell is prevented). In this way, the oxygen above thewater surface will quickly be absorbed by the water

in the well. Only nitrogen and water vapour, whichdo not oxidize the iron ions, will remain.

2. A diaphragm tank is used instead of a pressuretank. When there is an airtight diaphragm betweenthe water in the pressure tank and the air above it,the possibility of oxidation is also eliminated here.

When applying the above methods, the iron ions will notoxidize until oxygen from the air mixes with the ionswhen water is tapped. As the oxidation of the iron ionstakes time, most of the ions will not oxidize until theyare washed out into the sewage system where rustdoes not harm.

To complete the above-mentioned methods, a phos-phate feeder can be inserted between pump and pres-sure tank. The phosphate feeder may be of the tablet

type where part of the water is fed through a porouslayer of phosphate, or it may be a fluid feeder as men-tioned under chlorination.

Hermeticallysealed

Water is being tapped.The pressure in the diaphragm tankand the system pressure drop.

When the pressure is below the setswitch-on limit, the pump will start.

The pump has been stopped. Thediaphragm tank is filled with water andthe system is under pressure.

Membrane Membrane


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Fig. 62 Phosphate feeder installation


Phosphate passivates iron ions so that they do not oxi-dize.

Instead of a phosphate feeder, you may choose an ion-exchange unit which functions as mentioned underhard water. An ion-exchange unit for removal of iron inthe water has another type of resin than the one men-tioned under hard water.

If the content of iron in the water is higher than 1.5 ppm,the water should be aerated and filtered as follows:

Oxidize the iron ions.

Let the oxidized ions flocculate.

Remove the flocculated material from the drinkingwater by filtration.

Various types of pre-manufactured systems are avail-able on the market, but you may also build one yourself.First an oxidizing device must be built in. It can be doneby means of a small compressor which is activatedwhen the water pump starts. Then the compressor addsoxygen to the pumped water. Then there must be areaction zone where all the iron ions can react with theadded oxygen. When the iron has been oxidized, it willflocculate where the velocity is low, i.e. form small flocsconsisting of many oxidized iron ions. This flocculationzone is easiest to establish at the top of the filtrationtank.

Hermeticallysealed

In phosphate feeder installations,part of the water is directed throughthe feeder to dissolve somephosphate

Phosphate feeder

Membrane


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Fig. 63 Filter bed with backwashing installation


The top of the tank must be equipped with an automaticvent so that the air that has not been used can escape.The flocculated rust is easily removed by means of a fil-ter.

You can make a filter yourself in a tank with two largemanholes in the side. Porous Leca blocks (or anothersimilar inorganic material) are placed at the bottom ofthe tank. A 1520 cm layer of small stones with a diam-eter of about 1020 mm is put on top of this filter base.

Then a 6080 cm layer of filter sand ( 0.91.4 mm)completes the filter.

The flocculated rust will be detained in the top of the fil-ter whereas the non-flocculated iron ions will precipitate2040 cm down in the filter sand.

The filter sand should be cleaned of rust particles reg-ularly by pumping water into the bottom of the tankwhile the compressor pumps air into the water (back-washing). When the outlet in the top of the tank isopened, it will make the sand partic les in the filter sandvibrate whereby loose rust particles and flocs of rust are

flushed into the sewer system. When the filter has beenbackwashed, the water inlet at the bottom of the tankand the outlet at the top are shut off, and the filter willfunction as a new one again.

Aircompressor

Valve to beclosed for filterbackwash

Valve to beopened forfilterbackwash

Pressure tank

Filtra-tion

Floccu-lation

Reactionzone

Air inject ion

Automatic vent

Valve to beopened for filterbackwash

Drain valve


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Fig. 64 Result of iron bacteria in water

Red water (iron bacteria)

Symptoms

Red slime develops in sewage siphons.

Screens in taps may be blocked by slimy rust.

Red slime develops in toilet cisterns.

Pressure gauges do not function due to inlets beingblocked by slimy rust.

Cause

The well is infected with iron bacteria which willspread to the whole water supply system.

Screensblocked byslimy rust

Filters blocked byslimy rust

Wire meshes blockedby slimy rust

Red slime intoilet tank

Pressure gaugeinlets blocked byslimy rust


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Fig. 65 Installation for solving problems with iron bacteria

Red water (iron bacteria)(continued)

Iron bacteria can be moved from one place to anotherby aquifers and by the drillers equipment when he hasbeen working in an infected well. The easiest way tocheck whether there are iron bacteria in the water is toremove the cover of the toilet cistern. If bottom andsides have a slimy layer, the well is probably infected byiron bacteria.

Iron bacteria subsist on the iron in the water. If there areiron bacteria in the water, it is probably acid too. If so,the pipe system will be corroded, resulting in rust stainsin wash basin, bathtub and other places where watermay be dripping.

If the water contains iron bacteria, it cannot be purifiedof iron ions without killing the iron bacteria by chlorina-tion first. The well should be chlorinated directly, other-wise it will continue to produce bacteria and corrosionon casing, filter and riser main.

If the water in the well is acid, soda ash or caustic sodashould be added together with chlorine to make thewater neutral before filtration. One of the standard fil-ters available on the market may be installed, or youcan build one yourself in accordance with the guide-lines given above on page 79.

It is not essential to oxidize the water when you chlorin-ate as chlorine oxidizes the iron ions present. On theother hand, oxidation helps to improve flocculation ofthe oxidized iron ions.

Dosingpump

Solution

Sodiumhypochloriteand soda ash

Wellchlorination

Problem


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Fig. 66 Result of dissolved manganese in the water

Brownish-black water (Dissolved manganese)

Symptoms

White clothes turn brownish when washed.

Bathtubs, wash basins and toilets get brownishstains caused by dripping water.

Pots turn brown or black inside.

After a long period without water consumption, thefirst water which is tapped is black.

Coffee and tea taste bitter.

Causes

Dissolving action of water when it passes throughunderground layers containing manganese.

Acid ions in the water, even at normal pH values.

Blackish water is rather rare, but it occurs. More oftenbrownish water containing manganese and iron isfound. Even if the manganese content in the water is aslow as 0.1 ppm, there will be black stains in wash basin,toilet and bath tub.

Coffee and teataste bitter

Turns brown orblack inside

Brownish-black stains


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Fig. 67 Overcoming of difficulties caused by the existence of manganese in ground water

Brownish-black water(continued)

Manganese is removed from water in the same way asiron. Manganese bacteria exist like iron bacteria in thewater and subsist on the manganese ions. These bac-teria sho

domestic water supply manual - إمدادات المياه للوحدات السكنية

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