Water Supply and
pollution
By
Dr. Ashraf Hussain
Msc., PhD. Community Medicine
Water Supply
Although water is the most wonderful and most abundant nature’s compound but
only less than 1% of the world’s water resources are available ready for use.
WHO currently es mates that over 1.1 billion people worldwide lack access to
adequate supply of clean water.
Uses of clean water in the domestic setting:
1. Drinking and cooking.
2. Personal hygiene.
3. Cleaning e.g. cooking utensils.
4. Gardening e.g. garden vegetables.
QUANTITY
A daily supply of 150-200 litres per capita is considered as an adequate supply to
meet the needs for all urban domestic purposes.
QUALITY
The water should be free from chemical & biological contamination plus
being acceptable in terms of color, taste & smell in accordance with the WHO
Guidelines on the Quality of Drinking Water (1993).
Sources of Water
Ø
Surface water Ü It includes flowing water (streams and rivers) and still water
as (lakes, ponds and reservoirs).
Ø
Ground water Ü e.g. wells & springs.
Ø
Rain water.
Ø
Sea water
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Main sources of water supply & their impurities:
Rain water
Rain water is the purest water in nature.
Chemically, it is very soft water containing only traces of dissolved solids
rain water-gets impurities during it's fall to the earth. it absorbs from the
atmosphere gases (H2S,CO2, NH3, nitrogen & oxygen). Besides it absorbs
suspensions like (dust, soot and microorganisms).
Gaseous sulphur and nitrogen oxides emitted from power plants that use fossil fuels,
react with atmospheric water, forming dilute solution of sulphuric and nitric acid.
Such acidic rain has begun to have serious impacts on surface water quality and on
plants etc.
Near & at earth it
takes suspensions like bacteria, pollen, soot, bird droppings
& dust.
2. Surface water
It is the main source of water supply in many areas.
Surface water is prone to contamination from human and animal sources.
It is never safe for human consumption unless subjected to sanitary protection and
purification before use.
a. IMPOUNDING RESERVOIRS
These are artificial lakes constructed usually of earthwork or masonry in which large
quantities of surface water is stored.
One disadvantage of storing water for long periods in reservoirs is the growth of
algae and other microscopic organisms, which impart bad tastes and odours to
water.
The upland surface water derives its impurities from the catchment areas. the
sources being human habitations and animal keeping or grazing.
The general belief that mountain streams are very pure water is often untrue.
b. Rivers
Rivers furnish a dependable supply of water.
it is always grossly polluted and is quite unfit for drinking without treatment.
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The impurities of river water are derived from surface washings, sewage and sullage
water, industrial and trade wastes, and drainage from agricultural areas.
The customs and habits of the people like disposal of the dead animals, garbage and
other solid waste.
Self-purification does occur in river water by natural forces such as dilution,
sedimentation, aeration, oxidation, sunlight, plant and animal life but these agencies
are not sufficient to render the water potable.
Sea water
Although it is plentiful, it has great many limitations.
It contains 3.5 per cent of salts in solu on.
Continuous evaporation increases the dissolved impurities content, which is further
increased by the impurities thrown by rivers as they join sea.
Desalting and demineralization process involves heavy expenditure, so It is adopted
only in places where sea water is the only source available.
Ground water
Ground water is the cheapest and most practical means of providing water to small
communities.
It is superior to surface water, because the ground itself provides an effective
filtering medium.
The advantages of ground water are:
It is likely to be free from pathogenic agents,
It usually requires no treatment
The supply is likely to be certain even during dry season.
It is less subject to contamination than surface water.
The disadvantages are:
It is high in mineral content, e.g., salts of calcium and magnesium which render the
water hard
It requires pumping or some arrangement to lift the water
Ground water-include:
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springs : natural outlet of ground water held under pressure by the impermeable
layer.
wells - "are dug or driven holes to reach the underground water.
1. Shallow wells tap subsoil water i.e. the water from above the first impervious
layer in the ground.
2. taps water from the water-bearing stratum below the first impervious layer
in the ground
WATER POLLUTION
Pure uncontaminated water does not occur in nature.
It contains impurities of various kinds - natural and manmade.
The natural impurities are not essentially dangerous.
These comprise dissolved gases (e.g. nitrogen, carbon dioxide, hydrogen sulphide,
etc. which may be picked up during rainfall), and dissolved minerals (e.g., salts of
calcium, magnesium, sodium, etc.) which are natural constituents of water following
its contact with soil.
suspended impurities (e.g., clay, silt, sand and mud), and microscopic organisms.
These impurities are derived from the atmosphere, catchment area and the soil.
A more serious aspect of water pollution is that caused by human activity -
urbanization and industrialization.
The sources of pollution resulting from these are :
Sewage, which contains decomposable organic matter and pathogenic agents
Industrial and trade wastes, which contain toxic agents ranging from metal salts to
complex synthetic organic chemicals
agricultural pollutants, which comprise fertilizers and pesticides.
Physical pollutants, viz heat (thermal pollution) and radioactive substances
Chemical pollutants
These pollutants include detergent solvents, cyanides, heavy metals, minerals and
organic acids, nitrogenous substances, bleaching agents and dyes
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Chemical pollutants may affect man's health either directly or indirectly by
accumulating in aquatic life (e.g. fish).
The present concern about chemical pollutants is not only to their acute toxic effects
on human health but further the possible long-term effects of low level exposure,
which are often non-specific and difficult to detect.
Most of these pollutants are not easily removed by conventional water treatment or
purification processes
Water Related diseases
Man's health may be affected by the ingestion of contaminated water either directly
or through food; and by the use of contaminated water for purpose of personal
hygiene and recreation.
The term water-related diseases includes the following:
IMPURITIES OF WATER
The impurities present in water may be categorised into following categories:
(1) Dissolved Impuri es
(a) Dissolved gases: O2, CO2, H2S etc.
(b) dissolved salts:
Cations: Ca++, Mg++, Na+, K+, Fe++, Al+++ etc.
Anions: CO3–, Cl–, SO4–, NO3– etc.
(2)Suspended Impuri es:
(a) Inorganic: Clay and sand
Such impurities usually cause mechanical irritation of gastrointestinal tract & even
diarrhea. These suspensions are cleared by sedimentation or alum precipitation..
(b) Organic: Oil globules, vegetables, and animal material usually occur through
contamination of water by sewage , refuse, house waste
(3) Microscopic Ma ers as Bacteria, algae, fungi etc
HARDNESS OF WATER
Hardness is due to presence of certain salts of Ca2+, Mg2+ and other heavy metal
ions like Al3+, Fe3+ and Mn2+ in water.
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Temporary hardness: due to the presence of bicarbonates and hydroxides producing
metal ions as Ca(HCO3)2 and Mg(HCO3)2.
Destroyed by boiling
Ca(HCO3)
2
→ CaCO3 ↓ + H2O + CO2↑
Permanent Hardness: due to the presence of dissolved chlorides and sulphates as
CaCl2, MgCl2, CaSO4, MgSO4, FeSO4, Al2(SO4)3 etc.
Not destroyed by boiling.
Effects of Hard Water on health
Effect on health: It adversely affects digestive system causing diarrhea and increase
possibilities of forming calcium oxalate crystals in the urinary track on drinking.
Little hardness, give taste to water, better for teeth and bones, prevent lead
poisoning of water in old lead pipe system due to CaCO3 coat.
Treatment of Water Supply
In many instances some form of treatment will be necessary.
The degree of treatment will depend on the quality of the raw water sourced.
Surface water sources tend to require the greatest level of treatment whereas
ground water may not require any treatment at all in deep well.
Treatment may be as simple as boiling in the home or a series of activities resulting
in water fit for human consumption.
Depending on the quality of raw water the following are the stages of
treatment :
1. Flocculation, Coagulation and Sedimentation.
2. Filtration.
3. Aeration
4. Disinfection.
It’s purpose is to remove as much solid matter “such as suspended particulates”
from water as possible thus aiding the stages of filtration & disinfection.
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§
Filtration
The best known method of filtration is the passing of water through a combination
of small stones & sand, often described as SLOW SAND FILTRATION.
Filtration is aimed at not only removing remaining particulate matter but also
pathogenic organisms.
Filtration may also be used to remove chemical contaminants in water (e.g. filtration
of arsenic out of ground water).
Aeration
Aeration = removal of dissolved gases
Aeration = bubbling air through the water
Air bubbles absorb the other gases and remove them
O
2
in the air can oxidize some organics to CO
2
gas
CH
4
+ 2 O
2
----> CO
2
+ 2 H
2
O
Cheap and widely used purification step
Disinfection
The most common form of disinfection is chlorination.
disinfection is the last stage in the treatment process & is aimed at killing pathogenic
organisms in the water.
It is a supplement process not a substitute to filtration.
In municipal treatment plants chlorine gas is often used whereas on a small scale
other forms of chlorine are used such as granules or tablets.
Chlorine kills pathogenic bacteria, but it has no effect on spores and certain viruses
(e.G., Polio, viral hepatitis) except in high doses.
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Chlorine has several important secondary properties of value in water treatment
1. It oxidizes iron, manganese and hydrogen sulphide.
2. It destroys some taste and odour producing constituents.
3. It controls algae and slime organisms and aids coagulation.
Chlorine is consumed by organic matter & it is therefore important to remove as
much organic as possible from raw water before disinfection.
The stages of flocculation, coagulation, sedimentation & filtration are all aimed at
removing organic matter thus enabling administered chlorine to act on the
pathogens that remain.
Principles of chlorination : The mere addition of chlorine to water is not chlorination.
There are certain rules which should be obeyed in order to ensure proper
chlorination :
the water to be chlorinated should be clear and free from turbidity. Turbidity
impedes efficient chlorination.
the "chlorine demand" of the water should be estimated. "The chlorine demand of
water is the difference between the amount of chlorine added to the water, and the
amount of residual chlorine remaining at the end of a specific period of contact
(usually 60 minutes), at a given temperature and pH of the water".
In other words, it is the amount of chlorine that is needed to destroy bacteria, and
to oxidize all the organic matter and ammoniacal substances present in the water.
The point at which the chlorine demand of the water is met is called the "break-
point". If further chlorine is added beyond the break point, free chlorine (HOC! and
OCl) begins to appear in the water
Thirdly the contact period. The presence of free residual chlorine for a contact
period of at least one hour is essential to kill bacteria and viruses.
chlorine has no effect on spores, protozoa! cysts and helminthic ova, except in
higher doses.
The minimum recommended concentra on of free chlorine is 0.5 mg/L for one hour.
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This compares with the residual chlorine level found in swimming pools of 1.5 – 2
mg/L.
The free residual chlorine provides a margin of safety against subsequent microbial
contamination such as may occur during storage and distribution.
The sum of the chlorine demand of the specific water plus the free residual chlorine
of 0.5 mg/L cons tutes the correct dose of chlorine to be applied.
Testing of
Water Supplies
Testing of Water Supplies
When a new source of water supply is provided, the water from that source should
be tested for physical, biological & chemical parameters.
A sampling program for periodic testing should also be established for the purpose
of continuous monitoring.
The frequency of testing will be largely determined by the size of the population
served.
Testing of Water Supplies
The physical parameters to be looked at in determining a water supply’s suitability
are its color (turbidity), smell & taste.
Total dissolved solids: Total dissolved solids (TDS) can have an· important effect on
the taste of drinking water.
Water with concentrations of TDS below 1000 mg/litre is usually acceptable to the
consumers and if less than 600 mg/litre is generally considered to be good.
Drinking water becomes increasingly unpalatable at TDS levels greater than 1,200
mg/litre.
Water with extremely low concentrations of TDS may be unacceptable because of its
flat, insipid taste.
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Biological testing:
The key indicator of biological contamination in a water supply is the presence of
fecal coliforms (e.g: E. coli).
The presence of coliforms in numbers greater than 10 coliforms/100ml as
determined in the sphere standards indicates an unacceptable level of
contamination.
Faecal streptococci: in doubtful cases, the finding of faecal streptococci in water is
regarded as important confirmatory evidence of recent faecal pollution of water.
Cl. perfringens
On the basis of this test the water is classified as follows
Chemical Contaminations
There is whole range of chemical contaminations one can test for & just some of
them include nitrates, phosphates, fluoride, arsenic & iron.
The problem associated with chemical constituents of drinking water arise primarily
from their ability to cause adverse health effects after prolonged periods of
exposure.
Particularly are contaminants that have cumulative toxic properties, such as heavy
metals and substances that are carcinogenic.
Examples of these may involve lead, cadmium, mercury, cyanide and chromium
Reverse Osmosis
Reverse Osmosis
Osmosis = natural movement of water from high concentration to low concentration
through a membrane
Reverse osmosis = purification of water using high pressure to force water from low
to high concentration
Membrane only allows water, not ions, to pass due to size
Cellulose acetate is often the membrane compound
Ions removed: Na
+
, K
+
, Pb
2+
, Hg
2+
, NO
3
-
, PO
3
2-
Problems: expensive, wasteful (discard more H
2
O than keep)
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Ozone = O
3
gas used
Can’t be stored, so it must be made on site (expensive)
10 minutes contact with water will disinfect it
No residual protection
Effective against viruses (HOCl less)
May form toxic oxidized organics (formaldehyde H
2
CO)
UV light alters DNA and killing microorganisms
10 s irradia on is effec ve
Same effect UV light has on skin—cancer
Dissolved substances and colloids block light
Fluoridation of Water
Water fluoridation is the controlled addition of fluoride to a public water supply to
reduce tooth decay.
Fluoridated water operates on tooth surfaces: in the mouth, it creates low levels of
fluoride in saliva, which reduces the rate at which tooth enamel demineralizes and
increases the rate at which it remineralizes in the early stages of cavities.
In 2011 the World Health Organization suggested a level of fluoride from 0.5 to
1.5 mg/L
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