Lakew Desta(BSc.

,MPH)
 Chapter objectives

• After completing this chapter, students will be

able to
– Describe types of water associated diseases

– Describe water sources and requirements

– Discuss water impurities and their health impact

– Identify the steps of drinking water treatment

 Introduction
• Water is essential to sustain life. Without water, life
on earth would not exist.
• From the very beginning of human civilization, families
have settled close to water sources, along rivers, lakes
or near natural springs
• But some people live in areas where water is scarce
• Often women & children carry it over long distances,
particularly during dry periods
• Scarcity of water may lead people to use sources that
are contaminated. 3
Definition of Terms

Raw water
- Untreated water from suspicious sources such as rivers, lakes
or from unprotected wells and springs
Contaminated water
- Water which may contain harmful microorganisms or toxic
chemicals which make it unfit for use.
- Generally these contaminants can not be detected by the
organs of sight, taste and smell.

4
Polluted water

• Water that has come in contact with substances that

alter its physical qualities, so that it changes in color,
level of turbidity, taste or smell.

• Pollution can be detected by the sense organs.

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Clear water
– Water that has sparkling appearance to the eye
– Such water could be clean or contaminated
Clean water
– Water that is free of disease causing organisms
Palatable Water
– Water that is pleasant to drink
– It is not necessarily clean or potable
– It can be pleasant to drink, nevertheless may be
contaminated

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Potable water
• This is drinkable water
• Water which is free at all times from any harmful
substances (pathogenic organisms or chemicals).

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• Improved drinking-water sources: are likely to
be protected from outside contamination, and
from faecal matter in particular.
• E.g.
Piped household connections
public standpipes
Boreholes
protected dug wells
protected springs and rainwater collection.
• Unimproved water sources include:
unprotected wells
unprotected springs
surface water (e.g. river, dam or lake)
vendor-provided water
bottled water (unless water for other uses is
available from an improved source) and
tanker truck-provided water.
 Water associated diseases
Waterborne

• The pathogen is in the water

e.g. Cholera, Typhoid, Giardia

Water washed

• When water is inadequate

e.g. scabies, trachoma, conjunctivitis 10

 Water based

• The pathogen spends part of its lifecycle within

aquatic animal
• e.g. Schistosomiasis, Guinea worm(Dracunculus
medinensis)
 Water related

• The pathogen carrying insect is breading near the

water and bite near it

e.g. Malaria, Onchocerciasis

 Sources of drinking water
 Surface water
• Rivers
• Lakes
• Streams
• Ponds
 Ground water
• Well
• Spring
 Rain water
++++ Advantages and Disadvantages
12
 Adequacy and accessibility

• Not adequate<5Liter/capita/day

• Survival allocation- 7.5L/C/D

• Basic adequacy- 20 L/C/D

• Intermediate adequacy- 50L/C/D

• Optimum adequacy and access >100L/C/D within 1000m

or 30 minute distance travel(round trip)
Ethiopia – 20 L/C/D within 1000m or 30 minute round trip
distance travel 13
 IMPURITIES OF WATER

Pure water is not found under natural conditions.

 Impurities found from the earth are called inorganic

 Impurities found from the growth and decay of animals

and vegetable matters are called organic

• Impurities of water are found in two forms:

Suspended impurities

Dissolved impurities

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 Suspended impurities

• Are very fine Particles of insoluble matter:

 Microorganisms as a result of pollution of surface
water.
 Suspended solids that include solid and clay,
pesticide, etc.
Algae that grow in ponds, riverbanks and in still
water.
 Suspended solids generally cause taste, color or
turbidity (muddiness/ cloudiness of water)
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 Dissolved impurities
These are divided in to two: Gasses & Minerals

Gasses: All natural water contains dissolved

oxygen and in certain circumstances CO2, the
presence of CO2 & H2S (but not O2) will cause
acidity, H2S itself will give bad odor to the
water

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 Minerals: Most common dissolved minerals in water
are salts of calcium & magnesium that causes
hardness in water and sodium and potassium causes
alkalinity.

• Other minerals such as Pb, As, Hg, Cr are toxic & may
be dangerous when the water contains in excess of the
recommended limits
WATER QUALITY PARAMETERS
1. Physical
2. Chemical
3. Bacteriological

A. Physical
1. Color
• May be due to the presence of organic matter, metals (iron,
manganese) or highly colored industrial waste
• Aesthetically displeasing may also indicate pollution
• Desirable that drinking water be colorless
• Desirable limit 5 Hazen unit
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 2. Taste and Odor
• Mainly due to organic substances, Biological activity
or industrial pollution

• Taste buds in the oral cavity specially detect inorganic

compounds of metals like magnesium, calcium,
sodium, copper, iron and zinc

• Water should be free from objectionable taste and

odor.
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 3. Turbidity
• Caused by suspended matter

• Desirable limit for drinking water-5NTU

• High level turbidity shield & protect bacteria from the

action of disinfecting agents.

• Should be below 1 NTU when disinfection is practiced

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 B. Chemical
1. pH

• It is the measure of hydrogen ion concentration

• Neutral 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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 2. Lead
• Lead occurs in drinking water primarily from corrosion of lead
pipe and solders & faucets constructed with leaded brass,
especially in areas of soft or acidic water.

• Lead exposure across a broad range of blood lead levels is

associated with a continuum of patho- physiological effects,
including

 impaired cognitive performance, delayed neurological and

physical development,

• Action level-10 µg/dL in blood

 3. Mercury
• Mercury occurs in water primarily as an inorganic
salt, and as organic (methyl) mercury in sediments
and fish
• Sources of mercury include the burning of fossil
fuels, incineration of mercury-containing products,
past use of mercury-containing pesticides, and
leaching of organic mercury from antifungal
outdoor paints, as well as natural origins
• Inorganic mercury is poorly absorbed in the adult
GI tract, does not readily penetrate cells, and,
therefore, is not as toxic as methyl mercury.
 Mercury…
• Organic forms, such as methyl mercury, are readily
absorbed in the GI tract and easily enter the central
nervous system (CNS),causing death and/or mental and
motor dysfunctions.
• Organic mercury also easily crosses the placental barrier
of the fetus.
• Larger fish significantly bioaccumulate organic
mercury.
• Acceptable limit- Inorganic mercury are 2 µg/L,
 4. Arsenic
• Dissolution of arsenic-containing rocks and the smelting
of nonferrous metal ores, especially copper, account for
most of the arsenic in water supplies.

• In excessive amounts, arsenic causes acute

gastrointestinal damage & cardiac damage.

• Chronic doses can cause skin cancer

• USEPA estimated that 2 µg/L might be an acceptable

limit for arsenic in drinking water
 5. Nitrate and Nitrite
• Nitrate is one of the major anions in natural waters, but
concentrations can be greatly elevated due to leaching of
nitrogen from farm fertilizer or from feed lots or from
septic tanks
• Nitrite, or nitrate converted to nitrite in the body can cause
adverse health effects:
– induction of methemoglobinemia, especially in infants under
one year of age,------Blue baby syndrome
• Acceptable limits
– 10 mg/L for nitrate
– 1 mg/L for nitrite
 Nitrate…
• Infants Vs adults
– Nitrite is formed by reaction of nitrate with saliva, but in
infants under one year of age the relatively alkaline
conditions in the stomach allow bacteria there to form
nitrite.
• Up to 100 percent of nitrate is reduced to nitrite in infants,
compared with 10 percent in adults & children over one year of
age.

– Furthermore, infants do not have the same capability as

adults to reconvert methemoglobin back to hemoglobin
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 7. FLOURIDE
• Occurs naturally from fluoride containing rocks
• Problem of rift valley areas
• Long term consumption above permissible level can cause
o dental fluorosis (molting of teeth)
o Skeletal fluorosis
• Acceptable limit – not more or less than 1 to 1.5 mg/l
• Remedy :
1) De-fluoridation
2) Mixing Fluoride free water
3) Intake of vitamin C,D, calcium.

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 C. Biological
• Bacteria
– Single-celled microorganisms (< 0.2 µm) that possess no well-
defined nucleus and reproduce by binary fission, sensitive
to disinfection
• Virus
– Viruses are a large group of tiny infectious agents, ranging in
size from 0.02 to 0.3 micrometers (µm).
– Viruses belonging to the group known as enteric
viruses infect the gastrointestinal tract of humans and
animals and are excreted in their feces.
– Over 100 types of enteric viruses are known, and
many have been found in groundwater & surface
water.
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• Protozoa
– Protozoa single-celled organisms that lack a cell wall
and are typically larger than bacteria (up to 100
µm)

– Found in water as resistant spores, cysts, or oocysts ,

forms that protect them from environmental stresses
such as disinfection

– effective filtration & pretreatment can reduce their

density by 99%
Bacteria
Viruses
Protozoa and others
 Indicator organisms
• It would be difficult to monitor routinely for pathogens in
the water.
– Isolating and identifying each pathogen is beyond the
capability of most water utility laboratories
– the number of pathogens relative to other microorganisms in
water can be very small, thus requiring a large sample
volume.
• For these reasons, surrogate organisms are typically used
as an indicator of water quality.
– Total coliforms
– Faecal coliforms
 Standards

Essential bacteriological
•Characteristics NumberStandards
/ 100 ml
Treated water in • Fecal coliform zero
distribution system
• Total coliform not more than 10
 WATER TREATMENT
• Water treatment is process of removing all
substance which are potentially dangerous or
undesirable.
• It includes: Physical
Biological
Chemical treatments.
• The extent of treatment required to be given to particular
water depends up on the characteristics & quality of the
available water the quality requirements for the intended
use.
• Objectives
1. To remove water borne disease.
2. To remove substance which imparts.
3. To remove excess minerals.
4. To regulate essential chemicals.
5. To remove excess dissolved gasses.
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 CONVENTIONAL DRINKING WATER TREATMENT
UNITS
1. Preliminary water treatment units

2. Aeration

3. Coagulation

4. Sedimentation

5. Rapid sand filter

6. Slow sand filter

7. Disinfection
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 Conventional Surface Water Treatment

Steps of water treatment

Raw water

Screening Filtration

sludge sludge
Alum
Polymers Cl2
Coagulation Disinfection

Flocculation Storage

Sedimentation Distribution
sludge
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 Treatment of Water on a small scale
• For economic reasons, large scale water treatment
procedures are not existing and can not be practical for
poor communes in developing countries like Ethiopia.

• However, water- borne diseases are prevalent among

such communes because of consumption of untreated
water.

• Water must be adequately treated before

consumption, even in rural
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Lakew D. (MPH) 40
• Treatment of house hold water supplies may be effected
by the following methods, used singly or in
combination, depending on the reliability of each
method.

1. Boiling: Is one of the most reliable methods of

disinfecting water on a small scale provided it is
brought to the boiling point and is kept 15-20 minutes.

• All forms of microorganisms including the most resistant

spores or cysts can be destroyed using this method.
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2. Filtration: Using home- made sand filters or candle
(ceramic) filters.

• The filtering medium in the home made sand filter is the

sand as a physical straining method and biological activities
due to growth of microorganisms which takes place in the
top most layer of the sand grains soon after the filter is put
into operation.

• The microbial growth in the sand grains forms a stick

gelatinous coat in the top layers of the filer, and is called
schmutzdecke, a German term meaning “cover of filth”.
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• This filter may be made using barrels (drums)

• However, the sand filter can not be relied upon

to remove organisms like viruses and some of the
very small sized bacteria.
• Candle filters are commercially made for filtering
individual water supplies.
• The core of the filter is a porous cylinder (shaped
like a wax candle, hence the name), made from
high-quality porcelain.

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 Storage

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• The efficiency depends upon the pore size of the candle

• Different manufactures produce candle filters of varying

pore sizes (0.3-50microns)

• A micron is one millionth of a meter

• The average size of a bacterium however is about 1.5

micron may not remove all the pathogenic organisms
(e.g. viruses)

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2. Chemical disinfection: Chemical disinfection
compounds such as chlorine, iodine, silver salts and
potassium permanganate etc. May be used.
• Chlorine or its compounds are however cheaper and
commonly available.
• Three drops of 1% chlorine stock solution applied to
every liter of water can give satisfactory disinfection on
a clear water.
3. Storage and sedimentation
4. Exposure to sun-light: Exposure to Ultra Violate light
radiation (UV-radiation)

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 Locating and Developing Sources of

Water Supply

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I. Ground water (underground water)
• Ground water is that portion of the rainfall which has
percolated into the earth until it reaches an impermeable
stratum, a layer which it cannot penetrate.

• It can be abstracted through wells and springs.

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Advantage
a) Comparatively free from disease causing
micro- organisms.
b) If properly protected and treated
immediately after completion of
construction, it can be used without further
treatment.
c) It can be found near a family or a
community.
d) It is not exposed to evaporation

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Disadvantage

• It normally needs pumping unless from a spring

• In certain localities may contain excessive dissolved

minerals.

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• In terms of depths of occurrence of the
water–bearing stratum, groundwater may
be tapped by the following means.

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A. Shallow wells: Are wells that have been dug
into the uppermost permeable stratum

• They have a depth of less than 30 meters

• In shallow wells, the water level always stands

with in “sucking” distance of a pump located
at the top of the well

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B. Deep wells:
• Are wells that have been sunk through an
impermeable formation until they tap water
from a permeable stratum below it
• Sunk: drilling machines
• Minimum depth: 60 meters
• Constructed for large communities
• Mineral content: high
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C. Artesian wells:

• Wells in which groundwater gushes out of its

own accord above ground level

• In other words, an artesian well can flow

naturally, without any artificial efforts

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• An artesian well is formed whenever there is a
favorable hydraulic gradient for groundwater
to be at sufficient hydrostatic pressure to rise
above the zone of saturation

• In general these wells are not common.

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D. Springs:

• Are occurrences of groundwater naturally

issuing at points where the water table
reaches the surface, or where the top confining
layer over the water –bearing strata is broken

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• Springs are normally found at the:
– Foot of mountains and hills

– in lower slopes of valleys and

– near the banks of major rivers

• The yield (flow rate) of a spring varies with the

position of the water table, which in turn varies
with the rainfall amount at that locality and
season.
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Springs may be classified as:

1. Surface, intermittent or seasonal spring

2. Mainsprings

3. Thermal or hot springs

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Protection of ground- water from contamination
• The techniques of protecting ground water from
contamination are based on a good understanding of
the
– Geology
– Topography
– Drainage basin
– Vegetation
– Human habitation of the locality
• Since the most common methods of tapping ground
water are by wells (particularly dug wells) and springs,
we will be specific to these sources

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• The rate of contamination of ground water by
pathogenic organisms or by dangerous chemical
pollutants depends on the following factors:

a) The nature of the aquifer: in particular

permeability of the ground formation in relation to
contamination flowing towards the water.

b) The hydraulic gradient: the direction the ground

water moves.

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 C. The depth to the water table: if the water table is
high (near to the surface), there will be chance for
the pathogenic organisms to be filtered before
reaching the water table.

D. Distance from the source of contaminants: the

further away is the water source from sources of
contaminates (e.g latrines), less is the chance from
contamination.

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Development of wells

• A water well may be defined as a hole or a shaft sunk

into the earth’s crust to a depth below the free water
level or into deep-water-bearing strata for the purpose
of obtaining ground water.

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Ways In Which Well- Water May Be Contaminated.

• Taking a hand- dug well as a model, we find that the

water may be contaminated in the following ways:
a) Infiltration from nearby latrines, cesspools, septic
tanks, etc.
b) Surface water (flood) entering the well.
c) Pollutants carrying dirt and microorganisms may
fall into the well (insects, rodents, other small
animals, etc).
d) Use of unsanitary bucket and rope

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 Prevention Of Contamination of a Well
a. Proper sitting of the well:- The well should be sited on
a higher level from a source of contamination
(latrines, septic tanks, cesspools, etc).

– The hydraulic gradient should be from the well

towards the latrines ; and never vice versa

– In normal soil formations: the minimum distance

>15 meters.

 This rule, however, does not apply to limestone

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b. Protection of the well:
a) Casing: the inside wall with waterproof cement
work to a minimum depth of 3 meters from the
mouth of the well.
• The casing should also be extended for a
minimum of 60cm above the surrounding of the
well should be graded off to prevent flow of
storm into the well.
b) Cover: A concrete cover overlapping the casing
should be fitted to prevent entry of any sort of
contaminants into the well.
c) Sanitary drawing of water: Ideally a pump should
be installed and if pump is not affordable a sanitary
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bucket and rope method may be used with care. 69
Lakew D. (MPH)
 d) Fencing: The immediate area of the well should
preferably be fenced to keep animals away.

e) Diversion ditch: should be constructed at around

15 meters away to divert flood coming into the
well.

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 Development of spring

• A good spring is a sure source of water

• Good springs are not common but where they do exist they
should be seriously considered as a source of water.

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 The following factors should be considered
before developing a spring.

– Is the flow adequate for the needs, even in dry weather?

– Is the water with a satisfactory sanitary quality ?

– Is the spring located favorably for natural gravity flow?

– Can the spring be adequately protected from pollution

and contamination?

– Would it be easier, cheaper, and reliable to develop the

spring than drill a well?
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 Prevention Of Contamination Of A Spring
• Springs make ideal water sources for many
communities provided that they are carefully studied
before being developed.

• Springs, like wells, may be subject to contamination.

1. Sitting of the spring.

• Before deciding to develop a spring, a through sanitary

survey should be made to identify the actual and
potential sources of contaminants and the means to
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• The survey should also include to check adequacy of
the yield, particularly in dry seasons before
unnecessary investment.

• If the results of the sanitary survey are satisfactory,

the eye of the spring should be properly located to
impervious layer and protection actions take place.

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Protecting the spring
a) Concrete water proof protection box: To cup the
spring to prevent all actual sources of contamination.

b) Collection box (optional): in order to ensure adequate

protected storage of water supply.
– Installation of a faucet on the intake pipe should be
discouraged as this may divert the spring direction.

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 Faucet

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c) Screened over flow and intake pipes: to
prevent blockage of flow by small animals such
as frogs, or large pieces of gravel.

d) A diversion ditch: constructed around the

spring same to dug wells

e) Fenced: Similar to wells, the spring should

ideally be

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Thank You.