Introduction to water supply

By Woineshet B. (BSc, MPH in Environmental and

occupational health)

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 Course objective

At the end of this class the student will be able to;

Define some of terminology in water supply

Explain the importance of water

Differentiate types water-associated disease

Important property of water

List and describe the basic requirements for safe,

adequate and accessible drinking water
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 Introduction
• Water is essential for life

• An adequate, safe and accessible water supply

must be available to all people

• Improving access to safe drinking water can result

in tangible benefits to health

• Water is one of the factors which contribute to the

transmission of many diseases
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 Public health importance of water
• Water is a basic necessity for life unfortunately, not all water helps
human to survive

• Water from contaminated sources causes numerous diseases and

untimely deaths

• A satisfactory water supply must be available to all humans

• public water supply must be potable, palatable and wholesome.

• Water must not have disagreeable physical change and must be

hygienically safe.

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 Definition of terms
• Palatable water: water that is pleasant to drink because
its taste is good but it may not be safe.
• Potable water: safe for drinking, free from pathogens
which are introduced to the water through feces, dirty
containers, etc
• Raw water: water that has not been purified
• Free water: groundwater which can move without
hindrance in response to the force of gravity
• Turbidity: disturbed, muddy appearance of water.
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 Importance and use of water:
1. Physiological needs: 70% of our body by weigh , about 2.0-
2.5 L/D needs for survival with out water very hard most
food contains water: milk about 90%, fish about 80%;
Dehydration is the adverse consequence of inadequate water
intake
2. Domestic/ social use: cleaning, washing,
3. Recreational purposes: swimming, boating,
4. Economical: agriculture, transportation, power production,
industrial use, etc.
5. Cultural / Spiritual values : Tebel , Timket and praying
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 occurrence of water
• Water is the most widely occurring substance in the world

• Over 72% of the earth's surface is covered by water.

• Salt water: 97.5%

• Fresh water: 2.5%

• Of 2.5%:

– 0.3%: Lakes and rivers

– 30.8%: Ground water

– 68.9%: Glaciers and

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– permanent snows
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• Where do humans get water?

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 Sources of water
Ground water
 It is comparatively likely to be free from disease causing micro-organism is
by far the most practical and safe in nature
 It can be used without further treatment if properly protected
 The most important source of water supply for most rural communities
 It is not exposed for evaporation and is used as natural storage in
underground.
 It is most practical and economical to obtain and distribute
 Classified in to well and spring water
Disadvantages
 It needs pumping unless it comes from a spring
 It is poor in oxygen content
 It may contain excess amounts of dissolved minerals
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 Sources of water
• Ground water
Wells and springs

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 Surface water
 Is found non-uniformly distributed over the earth’s surface

 Rain reaches the surface of the earth, it becomes surface

H2O

 Is less naturally dissolved minerals

 Quantity & quality depend upon the conditions catchment

area

 Has to be polluted by industrial & municipal effluents

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 Sources of drinking water
Surface water
Lakes, reservoirs, rivers

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• Do you think that water from the river in
Figure 13.4 would be safe to drink? Is this
an example of a protected or unprotected
source?

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 Physically accessible
• Water must be within safe physical reach, in or
near the house, school or health facility.
Accessibility to safe water can be classified as
follows:
• No access
– The distance to the water source is more than one
kilometre or more than a 30-minute round trip.
– The amount of water collected is very low (often below
5 litres per capita per day).
• Basic access
– The water source is within one kilometre/30-minute
round trip.
– The amount of water to be collected on average is
unlikely to exceed 20 litres per capita per day.

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• Intermediate access
– Water is provided onsite through at least one tap
(at yard level).
– Average volume of water collected is
approximately 50 litres per capita per day.

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• Optimal access
– Supply of water is through multiple taps within the
house.
– Approximately 100–200 litres per capita per day or
more is available.
• daily minimum water requirement was
between 2 and 4.5 litres per person per day
according to climate conditions.

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 Sources of water
Rain water
• can be used for domestic purposes in areas
where there are no alternative sources of water

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 Ocean water
 Is unfit for human consumption even though it comprises the
largest portion of water on the earth's surface (75%)
 Is also too salty for irrigation and for domestic purposes
 To make the ocean water fit for different purposes
It must pass through desalination

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 Water impurities
Two types:
• Dissolved impurities (gases and dissolved
chemicals )
– Adverse effect Acidity, Hardness, Alkalinity ,Toxicity
, Methaemoglobnamia ,dental caries or mottling

• Suspended impurities :Microbes; solids Bacteria,

algae, eggs, cysts, protozoa, soil, silt, soot,
– Adverse effect Infection turbidity, taste, color, odor
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 Hardness of water
 Capacity of water for reducing and destroying the lather of
soap
Temporary hardness:
Is caused by the presence of salts dissolved in water,
primarily calcium and magnesium (Ca (HCO3)2, Mg
(HCO3)2)
Permanent hardness:
• Caused by the presence of Sulphates, chlorides and nitrates of
calcium and magnesium(Cl, SO4-2, CO3- of Ca, Mg, Fe,Mn)

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 Adverse effects

 Loss of soap & detergents

 Effects to kidney
 Scale formation on boiling
 Cardio vascular prevalence
 Decreases life fabrics
 Disturbance of GI tract (mgso4,)

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 Methods of softening
Temporary hardness:

• Boiling

• Use of hydrated lime, Ca (OH)2 in large scale.

Permanent:

• use of soda ash (Na2CO3) and

• Ion exchange method

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 Water, Health and Disease
• The saying “water is life” is found in many cultures around the world

• It under scores the fact that clean water is an absolute prerequisite for
healthy living

• A wide range of natural and human influences affects water quality

There are two main types of water pollution

1. Chemical pollution of water and diseases

include detergents, solvents, nitrogenous substances, dyes, ammonia, etc

2. Biological pollution of water and diseases

numerous pathogenic organisms

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 Diseases associated with water
• water-borne Diseases

• Water-washed Diseases

• Water-based Diseases

• Water-related Diseases

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 Water- borne Diseases
• Disease caused by drinking of water that is
contaminated by human or animal excrement
and contains pathogenic microorganisms

• E.g. cholera, typhoid fever, amoebic and

bacillary dysentery

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 Water- washed Diseases
• Diseases transmitted by in adequate water for
personal hygiene conditions and practices
• Examples of water -washed diseases are
– Dermatological disease such as scabies
– Ophthalmic disease such as trachoma and
conjunctivitis
– Louse-borne diseases such as louse borne typhus and
– relapsing fever.

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 Water-based diseases
• These are diseases caused by infectious agents that are
spread by contact with water

• The essential part of the lifecycle of the infecting agent

takes place from an aquatic animal

• Many of the diseases in this class are caused by worms

E.g. Schistosomiasis and Dracunculiasis(guinea worm)

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 Water-related diseases
• Water-related diseases are transmitted by
insect vectors that breed in or near water

• Infections are spread by mosquitoes, flies and

other insects that breed in water or near it.

e.g. Malaria, sleeping sickness, yellow fever,

onchocerciasis, etc.
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The four mechanisms of water-associated diseases and preventive
strategies
Water-associated Example Agent Preventive strategies
Diseases

1. Waterborne -Improve water quality

(faecal –oral) -Prevent usual use of other
a) Low infectious dose Typhoid, cholera Bacteria contaminated source
b) High infectious dose Bacillary dysentery Bacteria - Health education
2. Water-washed
a) Skin and eye Scabies, trachoma Spirochetes - Improve water quantity
b) Other Louse-borne fever Other -Improve water access.
agents - Health education
3. Water-based -Decrease need for untreated water
a) Penetrating skin Schistosomiasis Helminthes contact
b) b) Ingested Guinea worms Helminthes -Control snail population
-Improve quality of water
- Health education
4. Water-related -Proper site selection of house
a) Biting near water Sleeping sickness, Protozoa -Using personal protection materials
b) Breeding in water Malaria Protozoa -Destroy breeding sites of insects
-Decrease need to visit breeding site
- Health education
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 Objective of drinking water supply
To supply safe and wholesome water:
1. Microbiological safety
2. Removal of excessive and undesired chemicals
3. Addition of essential chemicals
4. removal of impurities that interfere with water
color, taste, transparency, and odor;
• Adequate supply for all purposes: cooking, washing,
personal hygiene,
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 Water treatment
• Drinking water should be essentially free of disease-
causing microbes, but often this is not the case.

• Using the best possible source of water for potable

water supply and protecting it from microbial and
chemical contamination is the goal

• The burden of providing microbial safe drinking water

supplies from contaminated natural waters rests upon
water treatment processes
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 Small-scale water treatment systems
Household- and community-level treatment and most likely to
be used in rural areas
It is appropriate when:
• A relatively small amount of water is obtained from a well or
spring and is collected and transported by hand.
• The source is contaminated and simple protective measures
can neither improve water quality nor stop the contamination.
• Community resources are inadequate to meet the cost of a
simple community treatment system and make it difficult to
develop a centralized treatment system
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 Small-scale water treatment systems
• Boiling

• Filtering

• Chlorine addition/ Chlorine Tablets/Halazone

Tablets. one tablet/litre, Wuha Agar

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 Boiling
 Is one of the most reliable methods of disinfecting water

 Water is brought to the boiling point, and is kept boiling

for 15 to 20 minutes, all forms of micro-organisms

 Is effective for all kinds of raw water, except toxic

 Is its flat taste, due to the loss of dissolved gases (CO2 &
O2) and minerals

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 Filtration
• Is a process of passing water through porous
materials

• Carried out by simple filtration systems, such as:

Homemade sand filters

Home candle filters

Stone filters

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 Chemical Disinfection
A) chlorine or its compounds

 Can be applied to disinfect water on a small scale

 3 drops of 1% chlorine stock solution applied to every liter

 Tablet forms of chlorine (dose:1 tablet per liter of clear water)

B) iodine and its compounds

 Have also been effectively used for individual water

 Iodine is believed to be a better disinfectant than chlorine

 Relatively expensive for ordinary use, and imparts to the waters

 Tincture of iodine (2%) applied at the rate of 2 drops per liter gives
satisfactory results
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 Large scale/ Municipal Water
treatment process
• May find it in larger towns and cities where there is a
network of pipes and pumps to distribute water from the
treatment works
• The main steps are Preliminary water treatment (The
source and intake of the raw water ,Screening ), Aeration
and pre-chlorination , Coagulation and flocculation,
Sedimentation Filtration , Post-chlorination and
Supplementary treatment
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 Large scale/ Municipal Water
treatment process

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 Main objective of water treatment
 To remove pathogenic organisms
 To remove substance which impart color, taste or odor
 To remove excess or undesirable chemicals or minerals
 To regulate essential elements or chemicals (e.g.
Fluoridation or defluoridation of water)
 To remove excess or undesirable dissolved gasses
Defluoridation is process of removing the undesirable
amount of fluoride

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 Water Quality Parameters

• Physical parameters

• Chemical

• Bacteriological

• Disinfectants Byproducts

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 Color
• May be due to the Presence of organic matter,
metals(iron, manganese) or highly colored
industrial waste

• Aesthetically displeasing

• Desirable that drinking water be colorless

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 Turbidity

• Caused by suspended matter

• High level turbidity shield and protect bacteria from the
action of disinfecting agents
• Desirable limit-5NTU
• Should be below 1 NTU when disinfection is practiced
• Permissible limit-10NTU

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 PH
• Is the measure of hydrogen ion concentration
• water pH-7
• Acidic water has pH below 7
• Basic water has pH above 7
• Desirable limit 6.5-8.5 Beyond this limit the
water will affect the mucous membrane and water
supply system

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 STANDARDS
Parameters Desirable Permissible limit
Nitrate mg/l 45 45
Chloride mg/l 250 1000
Flouride mg/l 1 1.5
Arsenic mg/l 0.05 0.05
Aluminium mg/l 0.03 0.2
TDS 500 2000

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 Fluorosis causes mottling of
children’s teeth
 Tooth decay is a very widely distributed chronic disease
 Mottled or spotted teeth, dental fluorosis, staining of the
enamel
 Optimum concentration is 0.8-1.2mg/l (WHO=1.5 mg/l)

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 Essential bacteriological Standards
• Ideally, drinking-water should not contain any
microorganisms known to be pathogenic or
any bacteria indicative of fecal pollution

Characteristics Number / 100 ml

Treated water in Feacal coli form

distribution system zero
Total coli form not
more than 10
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 RESIDUAL CHLORINE
• Chlorine added to water forms hypochlorite ions and
hypochlorite acids

• Chlorine demand: Quantity required for killing micro

organisms and reacting with ammonia, organic
compounds etc.

• Free residual chlorine: To take care of post

contamination

• Desirable – 0.2 mg / liter

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 Why worry about water supply?

• Water is a basic necessity for life

• Major pathway into the body for contaminants

• Easy to contaminate, difficult (costly) to

remediate

• Expensive to transport, necessitating local

supplies for most communities
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 Any Questions?

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