Environment science

1. 7/6/2023 1
Unit 2:
Community water supply

2. Introduction
• Water is essential for life.
• It is the medium in which
all living processes occur.
• About 70% of man’s
body – weight is water.
• In order to maintain this
level, a healthy man will
require an average of 2
liters per day.
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3. • Man can survive for
weeks without food, but
only a few days without
water.
• It is impossible to have a
clean and sanitary
environment without
water.
• The provision of safe
and adequate water
supply in a community
is therefore of the
greatest importance in
public health service.
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 In addition to the daily
maintenance of our bodies, water
also plays a key role in the
prevention of disease.
 Drinking eight glasses of water
daily can decrease the risk of
 colon cancer by 45%,
 bladder cancer by 50% and
 it can potentially even
reduce the risk of breast
cancer.

5. Factors influencing the amount of water used
are
• Cultural habits
• Socioeconomic status and standard of living
• Hygiene awareness
• Productive uses
• The charges for water
• The quality of the water as experienced by users
• Climate
• Availability
• Method of distribution

6. Definitions
Safe/potable water
 It is water that does not contain harmful
chemical substances, or microorganisms in
concentration that could cause illness in any
form (WHO)
Palatable
 Water which is pleasant to drink but may be
contaminated
Adequate water
 Sufficient for drinking, domestic & other
household purposes.
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7. Occurrence of water con’t
 75% of the earth’s surface is covered by
water
 96.5% is in the ocean
• Salty, unfit for consumption & irrigation
 2.53% fresh water
• Neither evenly distributed nor properly
used
 0.97% other
 0.8% usable portion of the total
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Occurrence of water

9. Principal features of hydrologic cycle
 Evaporation from vegetation, from exposed moist
surfaces, the land surface, and from water bodies.
 Precipitation: The moisture forms clouds, which
return the water to the land surface or lakes &
streams in the form of precipitation
 Runoff: When the rate of precipitation exceeds the
rate of infiltration, runoff occurs.
 Infiltration: the rain wets vegetation and other
surfaces and then begins to infiltrate into the ground.
 Lake/ocean: Water reaching streams, both by
runoff and from ground water discharge, moves to
the lake or ocean where it is again evaporated to
perpetuate the cycle.
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10. Properties of pure water
 Colorless
 Odorless
 Tasteless
 Density of one (at 40c).
 Boils at 1000c
 Freezes at 00c
 Universal solvent
 Any deviation from these characteristics should be
considered as an indication of impurity of the water.
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11. Uses of water
 Domestic
 Agricultural ( irrigation)
 Manufacturing
 Fish & wild life maintenance
 Navigation
 Power generation
 Construction
 Recreational
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12. Sources of water
i. Ground water : Wells, Springs and Borehole
ii. Surface water: Rivers, Streams, Lakes, Ponds
iii. Rain water: the purest source, if it is collected
using clean surface
iv. Sea/ocean water: Salty; unfit for consumption &
irrigation
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13. A. Ground water
Advantages
 Safer than surface water
 Reliable year rounds
 Cheaper
 Proximity to users
Disadvantages
 Excessive dissolved minerals
 Pumping
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14. Surface and underground water supplies

15. • During development of ground water factors
contributing to the contamination of ground
water should be considered.
• These factors are:
– Nature of the aquifer
– The hydraulic gradient
– Depth of the water table
– Distance from the source of contamination
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16. How far the intestinal parasites travel in the soil?
• The travel of intestinal, bacteria in dry soil is practically nil.
• Accompanied by leaching water the distance traveled varies with the
porosity of the soil
– Under normal condition the vertical down ward travel in reasonably
porous soil will not exceed 40cm and the horizontal travel is about
30cm
– In dense, reasonably compact soil, the vertical down ward travel is
about 30cm, and horizontally almost nil.
– Exceptional: water dissolves limestone appreciably, and contaminants
may travel unlimited distances in underground channels and caves in
lime stone formation.
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17. Prevention of contamination of a well:
Sitting of the well
The well should be sited on a higher level than
the sources of contaminants-privies, cesspools, etc
In normal soil formation, the minimum distance
between the well and the source of contaminant
should not be less than 15m (50 ft).
• This rule does not apply to a limestone
formation
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18. Protection of the well
• Casing: should be made water proof material
• a minimum depth of 3m from to top to down.
• a minimum of 60cm above the surrounding ground level,
• Cover:
• to prevent dust insects small animals, etc, from falling in to
the well
• Diversion ditch: to divert the run-off
• Sanitary bucket and rope if pump is not installed
• Fencing:
– The immediate area of the well should preferably by
fenced to keep animals away
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19. Prevention of contamination of a spring:
• Sitting of a spring:
– Sanitary survey i.e. complete, extremely careful
and detailed investigation of water supply system
in order to detect potential source of contamination
must be conducted
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20. Protection of spring
• Construction of protection box
• Construction of collection box
• Intake and overflow pipe should be screened,
• A diversion ditch with a radius of 10 to 15 meters
should be made around the protection box
• If possible the area surrounding the spring should be
fenced to keep off domestic and wild animals
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21. Surface water
 Surface water is liable for contamination
 Source of water pollutants
i. Point source
ii. Non-point sources
i. Point source
 Pollutants which enter a water way from a
specific point through a discrete pipe, ditch,
culvert etc.
 E.g. industrial discharges
 Relatively easy to collect and treat
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22. 7/6/2023 22
Major causes of stream & river pollution

23. ii. Non-point sources
 Pollutants which run off in to water ways from
broad areas of land rather than entering the
water through a discrete pipe
 Result from a variety of human practices :-
 Soil erosion
 Animal feedlot runoff
 Pesticides & fertilizers run off
 Urban street runoff
 Fallout of airborne pollutants
 In any case surface water should never be used
as a source of water supply with out treatment.
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Protection of streams from gross pollution:
 Avoiding or drastically reducing the dumping of
human and animal wastes, factory wastes etc.
 Zoning stream:
 Upper most section: drinking purpose
 Middle section: for washing and
domestic animals
 Lower section- for irrigation

28. Impurities of water
 Water is not absolutely pure in nature.
 It gathers impurities as it goes through
its natural cycle
 Impurities may be divided in two
i. Suspended impurities
ii. Dissolved impurities
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29. i. Suspended impurities
a. Microorganisms
 From air, soil
 Waterborne diseases
b. Suspended solids
 Minute particles of soil, clay, silt, soot , dead
leaves & other insoluble materials get into
water by erosion & drainage
 Taste, color & turbidity
c. Algae
 Minute plants that grow in stagnant water
 Taste, color & turbidity
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30. ii. Dissolved impurities
1. Gases  CO2, H2S, etc.
 CO2 cause acidity
 H2 S imparts bad odor & acidity
2. Minerals  During percolation & dumping
 Ca & Mg cause hardness
 Na & K cause alkalinity
 Pb, As, Cr toxicants
3. Plant dyes
 Originate from plants which grow in or a round
water
 Causes acidity & color
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31. Diseases associated with water
 80% of all diseases &
 1/3 of the deaths in developing countries are
associated with unsafe water
 Diseases associated with water can be broadly
classified in to 5 epidemiological groups:-
i. Water borne disease
ii. Water washed disease
iii. Water related disease
iv. Water based /impounding disease
v. Excess/shortage of chemical constituents
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32. Water supply
1. Water borne disease:
• Caused by ingestion of contaminated water by human or
animal excrement, which contains pathogenic microorganisms.
Eg, cholera, typhoid, bacillary dysentery etc
• In addition it can be caused by the pollution of water by
chemicals, that have an adverse effect on health.
• Nitrates from fertilizers, DDT, Lead and other heavy metals
• Water treatment chemicals
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33. 2. Water washed disease
 Due to lack of adequate supply of water &
poor sanitation (personal hygiene)
 Eye infections : trachoma, conjunctivitis
 Skin infections: scabies & ring worm,
 Body louse : typhus, & RF
 other flea, & tick-borne diseases.
 Adequate supply of water
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34. 3. Water related disease
Water serves as development & breeding site of insects
 Filariasis, malaria, onchocerciasis,
trypanosomiasis & yellow fever
 Water management
4. Water based /impounding disease
 Caused by infectious agent come in contact with
contaminated water
 Diseases caused by parasites found in intermediate
organisms living in contaminated water
 Schistosomiasis, dracunculasis
 Water management
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35. 5. Excess or shortage of chemical constituents
E.g. Fluoride
 Excess dental fluorosis (mottled teeth)
 Shortage  dental caries (tooth decaying)
E.g. Calcium and Magnesium- hardness to
water
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36. Class exercises
Can you categorize these diseases
• Trachoma, Schistosomiasis, typhus, & other
flea, lice & tick-borne diseases, Cholera,
typhoid fever, bacillary dysentery, infectious
hepatitis A, onchocerciasis, amoebiasis,
&other diarrheal diseases, Filariasis,
dracunculasis, malaria, scabies,
trypanosomiasis & yellow fever
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37.  In planning a community water supply the
following parameters should be considered
to Prevent diseases associated with water
1. Quality
 Safe & wholesome (M/Os & chemicals)
2. Quantity
 Adequate & continuous
3. Convenience
 Accessible & Affordable
4. Water management
Presence of WaSHCo’s
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38. Quality Critical Parameters
Parameter Recommended level
Faecal coliforms 0 per 100ml(Nil)
Turbidity <5NTU
Disinfectant
residual
0.2-0.5mg/l
pH 6.5-8.5

39. Indicators definitions
 Accessability: time/distance
 Adequateness: availability/quantity
 Coverage:
% with improved water supply (HH connection,
public standpipes, protected underground water
sources, rain water collection)
Quality of water:
 biological/physical/chemical
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40. Table. Service level and quantity of water collected:

41. What is the coverage of safe water supply?
• In Ethiopia seems to be on track to reach the MDG target of having the population
access to clean water by 2015.
• Access to safe drinking water increased from 19% in 1990 to 68.5% in 2009/10
according to MOH report.
– in rural areas with access to clean water has significantly increased from 35%
in 2004/05 to 65.8% in 2009/10,
– compared to increases from 80% to 91.5% in urban areas for the same period
• Ethiopian condition access to improved drinking water sources:
53.7% coverage [EDHS 2011, CSA] 34.4%: piped water; 19.1%: protected ground
water source (wells, springs)
Urban: 94.5% Vs Rural 41.7%
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42. What is water treatment ?
 Process of removing all those substances
whether biological, chemical or physical
which are potentially dangerous or
undesirable in water supplies for human &
domestic use.
 it is generally easier to prevent water
getting dirty than it is to make it clean after
wards
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43. Objectives of water treatment
1. To remove pathogenic organisms &
consequently to prevent water-borne diseases
2. To remove substances which impart color, taste
or odor to the water
3. To remove excess/undesirable
chemicals/minerals
4. To regulate essential chemicals which may be in
excess or lacking in a certain water-supply
system,
 E.g. fluoridation or defluoridation of water,
5. To remove excess/undesirable dissolved gases
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44. Treatment of water can be conducted
i. At small scale level (home made)
ii. Large scale level (municipal water
treatment).
i. Municipal water treatment process
 Depending on the types of water sources,
 The treatment plant procedures are different.
 Surface water Vs Ground water
treatment methods
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45. Flow of municipal water treatment method
Flow Diagram
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Raw water Course
screen Fine screen Pumping station
Filtration
Sedimentation
coagulation
Aeration/pre
chlorination
Distribution
system/Reservoir
Chlorination

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Surface Water Treatment

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Groundwater Treatment

48. Aeration
Addition of air, to remove substances which cause
odor/taste E.g. Dissolved iron, manganese, H2S
Coagulation & flocculation
 To remove turbidity, color, bacteria through the
aid of coagulant
 Coagulants -Aluminum sulfate (alum), ferrous
sulfate, Ferric chloride, and some plant seed (e.g.
Moringa olifera)
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49. Sedimentation
 water is made quiescent for a given period to
remove turbidity, substances which cause color ,
taste, odor, bacteria
Filtration
 Trapping all suspended and colloidal matter and
collect clear water
Disinfection
 use of disinfectants like cholrine, idoine, potassium
permanganate, etc to prevent microorganisms.
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50. ii. Treatment of water on small scale
A. Boiling
B. Home made sand filters
C. Candle filter
D. Use of direct sunlight radiation
E. Chemical disinfectants:-Chlorine
and Iodine
F. House hold water storage
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51. Boiling
 Boiling for 15-20 minutes
 But it can not destroy toxic chemicals
 It doesn’t have residual effect
 It needs additional resources/energy
/time
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52. Home made sand filters
 Can be set up in individual homes, in
containers such as steel barrels, drums, etc.
 Properly constructed home made sand filter
can remove most of the substances that
cause turbidity, taste, and odor, the cyst
and ova of parasites, & other relatively
larger organisms.
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56. Candle filter
 Commercially made for filtering individual
water supplies
 Efficiency of filtration depends on the pore
size of the candle
 Pore size varies from 0.3µm-50 µm
 Viruses & small sized bacteria may not be
removed
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Disk Candle Pot
Filter Media/Element
Filter System

58. Chemical disinfectants
a. Chlorination
 Stock solution (1% chlorine)
• 3 drops of 1% chlorine / liters of water
• Minimum contact time is 30 minutes.
 Tablets (Halazone, aquatab etc.)
– 1 tablet (4mg)/ L clear water
b. Iodine
• 2 drops of 2% iodine /liter
• 1 tablet per liter
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61. Use of direct sunlight radiation
(SODIS)
 A 5-6 Hrs sunlight radiation exposure
for water Rx
 Half blackened container & half
transparent plastic/glass bottle
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 Sunlight kills M/Os & could be
used for water disinfection
 Plastic bottles are often available as a
waste product & could be used for a
new water Rt method
Solar Disinfection (SODIS)

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How to Use SODIS ?

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65. House hold water storage
 Water is stored for 72 hours or more
 Many organisms such as cercaria &
coliform bacteria can be reduced in
number
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However, chlorine and its compounds are the
disinfectant of choice, because:
Easy to handle, transport, and available
Comparatively cheap
Effective and long lasting
Simple to apply and
 Relatively easy to detect in water

67. Factors that influence the disinfecting power of chlorine &
its compounds
• The pH of the water
• Acidic  high disinfecting power (need less Cl2)
• Alkaline  less disinfecting power ( need more Cl2 )
• The quality of the water: More pollutants more Cl2 is required
to disinfect
• Contact time: 20-30 min- for effective & reliable disinfection
• Water Temperature: High T0 high disinfecting power
• Presence of ammonia: When Cl2 is added to water containing
NH3 or organic nitrogenous compounds  chloramines is formed
which has similar disinfecting power as Cl2 except that it is weak
& needs more contact time.
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68. Methods of calculation of chlorine dose
• Too much chlorine is poisonous and
• Too little is unreliable in disinfecting water.
• An exact dose must therefore be determined for
chlorinating a given water supply.
• Generally chlorine is applied at the rate of from
2 to 3 ppm, depending on quality of the raw
water.
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69. Supplementary water treatment
Hardness Removal (softening) 
• There are two categories of hardness:
• Carbonate hardness, which is due to bicarbonates of Ca and
Mg, and
• Noncarbonate hardness, which is due to Ca and Mg
chlorides.
• Hardness is responsible for increased soap consumption and
scale formation in pipes.
• Water softening is the removal of Ca and Mg hardness by
– by boiling, adding lime, adding Na2CO3, Ion exchange
resins
• Fluoridation: adding fluoride eg CaF
• De-fluoridation: removing Fluoride. Eg bone char.
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70. Water quality
–A water quality must be determined in terms
of:
• Bacteriological
• Chemical and
• Physical examination supported by a
thorough sanitary survey of the watershed
areas.
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71. Types of water quality examination
1. Physical examination: to determine aesthetic quality
2. Chemical examination: To test for chemicals which affect
the water quality and/or which are indicative of pollution
3. Bacteriological examination: To test for the presence
of bacterial indicators of pollution and hence safety for
consumption
4. Biological examination: To determine the causes of
objectionable odors, clogging of filters, etc.
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72. Water quality control
Characteristics of water, Safe or bad, that related to
acceptability for drinking .“WHO”
Water should be:-
1. Free from pathogenic microorganisms
2. No chemicals that have an adverse effect on
Human health
3. Fairly clear: low turbidity
4. Not saline
5. No chemicals that cause an offensive taste /smell
6. Not causing corrosion on water supply system, nor
staining clothes washed in it
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73. Some relevant water quality parameters
Temperature
Turbidity
Odors & tastes
Color
pH
Alkalinity & acidity
Chlorides
Nitrogen compounds (organic N, ammonia N,
nitrite N, nitrate N)
Hardness
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74. Some relevant water quality parameters con’t
Fluorides
Iron & manganese
Sulfates
Residual Chlorine
Total dissolved solids (TDS)
Dissolved oxygen (DO)
Biochemical oxygen demand (BOD)
Chemical oxygen demand (COD)
Coli forms
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75. Water quality parameter Measure as Highest
desirable level
Maximum
permissible level
TDS (total dissolved
solids)
mg/l 500 2000
Turbidity NTU 5 25
Colour mg pt/l 5 50
Iron mg Fe2+/l 0.1 1.0
Manganese mg Mn2+/l 0.05 0.5
Nitrite mg No-
3/l 50 100
Nitrate mg N/l 1 2
Sulphate mg SO42-/l 200 400
Fluoride mg F-/l 1.0 2.0
Sodium mg Nat/l 120 400
Lead mg Pb/l 0.05 0.1
Mercury mg Hg/l 0.001 0.005
Chromium(hexavalent) mg Cr 6+/l 0.05 0.1

76. The following table summarizes the National Secondary Drinking Water
Regulations, secondary standards. (EPA recommends secondary
standards to water systems)

77. Thank you