08. Water Hygiene and Hygiene of water

The lecture
Water Hygiene and Hygiene of
water-supply of inhabited
Author: Lototska O.V.
Water is a chemical substance. Its molecule
contains one oxygen and two hydrogen
atoms connected by covalent bonds. Water
is a liquid at ambient conditions, but it often
coexists on Earth with its solid state, ice,
and gaseous state (water vapor or steam).
•Water covers 71% of the
Earth's surface; the oceans
contain 97.2% of the Earth's
Every organism consists mostly of
water. The human body is usually
made up of 50 to 75 percent water. All
living things need a lot of water to
carry out their life processes.
Functions of Water in the Human
Water is essential for digesting food. It is also important
for getting rid of various toxic elements from the body, in
the form of urine, sweat and fecal matter.
Water helps to cushion our joints and prevents shocks in
Water present in blood is the carrier of oxygen and
nutrients to all our body cells.
Water present in lymph (a fluid that is part of our immune
system) helps the body to fight against various diseases.
Water helps to regulate and maintain our body
temperature. That explains why wet poultices are used to
cure fevers.
Water prevents dehydration and thus, helps to maintain
proper metabolism in our body.
Uses of water
Domestic Use:
7 % of water
washing, bathing etc.
Recommended need
of water is 120
liters/day/person. It
includes all aspects of
life which a person
has in his routine life
i.e bathing, washing,
drinking & for toilet
Public purpose: Water is required for public
cleansing, maintenance of gardens, and swimming
pools and other civic activities.
Industrial Use: 23 % of available water is used in
Agricultural Use: 70 % of available water is used
for growth of food and raw materials required.
Epidemic and toxicological
significance of water
Water can participate in spread of infections in the
following ways:
- as transfer factor of pathogens with the fecal-oral transfer
mechanism: enteric infections of bacterial and viral origin
(typhoid, paratyphoid А, В, cholera, dysentery,
salmonellosis, coli-entheritis, tularaemia /deep-fly or rabbit
fever/, viral and epidemic hepatitis А, or Botkin disease,
viral hepatitis E, poliomyelitis and other enterovirus
diseases, such as Coxsakie, EСНО etc.); geohelminthosis
biohelminthosis (echinococcosis, hymenolepiasis); of
protozoal etiology (amebic dysentery (amebiasis),
lambliasis); zooanthroponosis (tularemia, leptospirosis and
as a transfer factor of pathogens of the
skin and mucous membrane diseases (when
swimming or having another contact with
water): trachoma, leprosy, anthrax,
contagious molluscum, fungous diseases
(i.e., epidermophytosis);
-as the habitat of disease carriers –
anopheles mosquitoes, which transfer
haemamoeba and others (open water
Toxicological role of water consists in it containing chemical
agents that may negatively influence people health causing
different diseases.
They are divided into chemical agents of natural origin,
those, which are added to water as reagents and
chemical agents, which come into the water as the result of
industrial, agricultural and domestic pollution of water supply
Insufficient or non-effective treatment of such waters at
waterworks procures the continuous toxic effect of small
concentrations of chemical agents, or, rarely, in cases of
accidents and other emergency situations – acute poisonings.
Chronic (long term) exposure to Fluoride in water above
1.5 - 2 mg/liter can result in coloration of the teeth
(fluorosis). At higher levels, more severe impacts can
result including alteration of bone density resulting in
arthritis and tooth damage.
Mild fluorosis looks like this:
Balneal role of water
Water is used in medicinal purpose for
rehabilitation of convalescents (drinking of mineral
waters, medicinal baths), and also as tempering
factor (bathing, swimming, rub-down).
Domestic and economic role of water
Sanitary-hygienic and domestic functions of water
- water usage for cooking and as a part of dietary
- usage of water as means of keeping body, clothes,
utensil, residential and public premises and industrial
areas, settlements clean;
- sanitary-transport and disinfection functions of water –
disposal of residential and industrial waste through sewer
system, waste processing on plants, self-purification of
water reservoirs;
- watering of the
green areas within
fire fighting,
pollution clearing
(rain, snow).
Economical functions
of water:
-usage in agriculture
(irrigation in crop and
greenhouses, poultry
and cattle breeding
-industry (food,
chemical, metallurgy
- as the route of
passenger and cargo
Sources of water
Sources where water may be obtained include:
•Ground water
•precipitation which includes rain, hail, snow, fog, etc.
•surface water such as rivers, streams, glaciers
Prime source of all water.
Part of rain water sinks to form ground water, part of
it evaporates and some runs in streams and rivers.
These events are called "water - cycle".
Purest, bright & sparkling
colour, soft water, only traces
of dissolved solids, corrosive
action on lead due to softness,
in clean areas rain water is free
of pathogens.
Picks up local impurities such
as dust, soot, micro-organisms,
CO2, N2, O2, Ammonia &
Sulphur. In areas where NO2
and SO2 are present in
becomes acidic and the rain is
called acidic rain.
Surface water mostly originates from rain water.
It has highest chance of being polluted particularly river
water because people near banks throw wastes in it.
Sources of surface water are.
a. Impounding reservoirs
b. Rivers and streams
c. Tanks, ponds and lakes.
It is in form of:
a. Wells —
Deep well, shallow well,
Artesian well.
b. Springs — Seasonal springs, thermal
springs, mineral spring, shallow springs,
and deep springs.
The advantages of ground water are:
It is usually free from pathogenic agents.
It usually requires no treatment.
Its supply is continuous.
The disadvantages of ground water are:
It is high in mineral contents
It requires pumping or some arrangement
to lift the water.
A spring is
ground water
which finds its way
to the surface
because of
features. Cracks
present in earth,
water enters and
comes out from
other opening at a
low level. So
source may be
quite far away
such as 100-200
These are artificial holes
or pits dug into the earth
to reach the underground
water level. They
constitute a very
important source of
water supply in villages.
There are four varieties
of wells:
There are four varieties of wells:
1. Shallow Wells,
2. Deep Wells
3. Artesian Wells are a
variety of deep wells in
which water under
great pressure comes
out to the surface
4. Tube wells,
popularly known as
Abyssinian Tube
Wells are really
shallow wells
which are bored
by simply driving
iron pipes 3.8 to
5 cm in diameter
and 6 to 7.62
metres deep to
tap the ground
water. A pump is
attached to the
pipe to draw the
Types of aquifers and wells.
In a water table well, the water table is at atmospheric
pressure. In an artesian well, the water pressure is greater
than atmospheric. In a flowing artesian well, the water
pressure is such that it can flow freely above the ground
The population should be provided not
only with enough of water, but also
with qualitative water. Water should
not cause any pathological change in
the organism, should not cause of
spread of infectious diseases, and also
not to cause unpleasant sensations.
Waters, used for drink and everyday needs,
must correspond to the demands:
good organoleptic properties: refreshing temperature,
transparence, colorless, no smell and no taste .
harmlessness of its chemical composition
the absence of pathogenic microorganisms
safety in the radiological attitude
The pollution of water sources represents the
important ecological problem. Depending on type
of pollution there are:
 chemical,
 physical (radioactive substances, hot water),
 bacterial, virus and biological.
 Industrial wastewater is characterized by
considerable quantity of components.
Major categories of water pollutant
1. Infections agents - Bacteria, viruses
2. Organic chemical - Pesticides, plastics,
detergents, oil, and gasoline
3. Inorganic chemicals - Acids, caustics, salts,
4. Radioactive materials - Uranium, thorium,
cesium, iodine, radon
Hazards of Polluted Water:
1. Biological Hazards
These are due to some specific agent that causes illhealth.
Typhoid, Bacillary dysentery,
Cholera etc.
Viral hepatitis A & E,
Amoebiasis, Giardiasis.
Round worm, whip worm,
hydatid disease
Weil's disease
Guinea worm.
2. Other Hazards
a. GIT disturbances due to Na ++,
Mg ++ & Ca++ ions, e.g) increased
MgSO4 lead to diarrhea.
b. Lead poisoning
c. Iodine deficiency
d. Fluorine deficiency
e. Hardness of water
f. Infant methaemoglobinemia.
Impure water may be purified by either of
the following methods:
A. Natural
(a) Pounding or Storage.
(b) Oxidation and Settlement.
B. Artificial
I. Physical
II. Chemical
Disinfection or Sterilization.
III. Filtration
"Biological" or "Slow Sand" Filtration.
"Rapid Sand" or "Mechanical" Filtration.
Domestic Filtration.
Purification of water is of great importance in
community medicine. It may be considered under two
Purification of water on large scale
Purification of water on small scale
Three main steps in purification of water
on large scale:
Storage, Filtration, Chlorination
1. Storage:
Water is drawn out from source and
impounded in natural or artificial reservoirs.
Storage provides a reserve of water from which
further pollution is excluded.
Physical — About 90% of suspended impurities
settle down in 24 hours by gravity.
 Chemical — The aerobic bacteria oxidize the
organic matter present in water with the aid of
dissolved oxygen. As a result the content of free
ammonia is reduced and a rise in nitrates occur.
 Biological — 90 % of total bacterial count drops in
first 5 - 7 days.
2. Filtration
Filtration is important because 98 – 99
% of bacteria are removed by filtration, a
part from other impurities. Two types of
filters are in use, they are:
a. Slow sand filters (biological filters)
 b.
Rapid sand filters (Mechanical
Slow sand filter
 Supernatant
(raw) water:
 Sand bed
 Vital Layer
 Under drainage system
Filter control valves:
The filter is equipped with certain valves and devices which
are incorporated in the outlet pipe system maintaining a
steady rate of filtration.
When the vital layer
resistance to the passage of
water is increased the
supernatant water is drained
off Sand bed is cleaned by
scrapping of the top portion of
the sand layer to a depth of 1
- 2 cms. Scrapping is done 20
- 30 times.
The process is known as
Filter Cleaning.
b. Rapid Sand Filter
Rapid sand filters are of two types,
the gravity type and the pressure type.
Both the types are in use.
Filter Beds:
Back - Washing:
Rapid sand filters need frequent washing daily or
weekly. Washing is accomplished by reversing the flow of
water through the sand bed, which is called "back-washing".
Back - washing dislodges the impurities and cleans up the
sand bed.
The following steps are involved in the
purification of water by rapid sand filters.
i. Coagulation:
ii. Rapid mixing:
iii. Flocculation:
iv. Sedimentation:
v. Filtration:
How is water treated?
Coagulation: Alum and other
chemicals are added to water to form
tiny sticky particles called "floc" which
attract the dirt particles.
Sedimentation: The
heavy particles (floc)
settle to the bottom
and clear water
moves to filtration.
Filtration: The water
passes through filters that
help to remove smaller
Disinfection: A small
amount of chlorine is
added to kill any bacteria
or microorganisms that
may be in the water.
Water is placed
in a closed tank
where it flows
to homes and
the community.
Chlorination is the process in which chlorine is
added to water for purification. Chlorination-is more
effective when pH of water is around 7.
Effects of Chlorine:
a. Chlorine kills pathogenic bacteria, it has no effect on
spores and certain viruses.
b. It has germicidal effects.
c. It oxidizes iron, manganese and Hydrogen sulphide
d. If destroys some taste and odour producing
e. It controls algae and slim organisms
f. It aids coagulation
Action of Chlorine
When Chlorine is added to water, there is formation of
hypochlorous and hydrochloric acid. The hydrochloric acid is
neutralised by alkalinity of the water. The hypochlorous acid
ionizes to form hydrogen ions and hypochlorite ions as follows.
H2O + CI2
H+ + OCI-
The disinfecting action ofchlorine is mainly due to hypochlorous
acid and to a small extent due to hypochloriteon.
Principles of Chlorination
First, water should be clear and free from turbidity.
Chlorine demand of water should be estimated.
At least one hour is essential as a contact period of
free residual chlorine for killing bacterial and viruses.
Minimum recommended concentration of free
chlorine is 0.5 mg/L for one hour.
The sum of the chlorine demand of the specific water
plus the free residual chlorine of 0.5 mg/l constitutes the
correct dose of chlorine to be applied.
Agents alternative to Chlorination
The ozonization of water
Ozone contains three oxygen atoms. It is destroyed in
water, forming atomic oxygen: O3 → O2 → O. ozonization
is one of the best methods of disinfection: water is well
disinfected, organic admixtures become destroyed,
organoleptic features are improved. Water becomes blue
and it is equated with spring water.
Ozone dose is 0,5 - 6 mg/l. Sometimes, higher doses
are necessary for the lighting of water and improving other
organoleptic features. The time of disinfection is 3-5 min.
The remaining ozone should make up 0,1 – 0,3 mg/l. The
concentration of the remaining ozone 0.4 mg/l provides the
reliable inactivation of 99 % viruses for 5 min.
Asaka Water Purification Plant
Ozone has been used in water treatment since 1903. It is more
effective against bacteria and viruses than chlorine and adds no
chemicals to the water. Ozone cannot be stored and requires an
on-site ozone generator. In general, ozonation equipment and
operating costs are higher than other treatment procedures
Advanced Water Purification System
Ultraviolet Light
Ultraviolet irradiation will kill bacteria by creating
photochemical changes in its DNA. No chemicals are added to
the water by this process. Most ultraviolet water treatment
units consist of one or more ultraviolet lamps usually
enclosed in a quartz sleeve, around which the water flows.
The UV lamps are similar to fluorescent lamps and the quartz
sleeve surrounding each lamp protects the lamp from the
cooling action of water. The killing effect of the lamp is
reduced when the lamp temperature is lowered. Ground water
is usually a constant temperature year round and so it is
possible to set a flow rate that will not lead to excess cooling.
The effectiveness of UV irradiation depends on
• the intensity of the light,
• depth of exposure and
• contact time.
Water passes in a relatively thin layer around the lamp;
therefore, water flow must be regulated to ensure that all
organisms receive adequate exposure. If the water is at all
turbid, or if it contains traces of iron, the effectiveness of UV is
greatly reduced. In such cases, the water needs to be filtered
before it reaches the UV system.
The maximal bactericidal effect is achieved by the waves
250-260 nm, which pass even through the 25 cm layer of
transparent and decolorized water.
The disinfection proceeds very quickly: vegetative forms
of microorganisms die in 1-2 min. The turbidity, colour and iron
salts decelerate the disinfection, decreasing the transparence of
water. Consequently, it is necessary to light and decolorize
water before the disinfection.
There are some advantages of
irradiation over the chlorination:
bactericidal rays don't denaturate the
water and don't change its organoleptic
 they have wider biological action.
 Their bactericidal action is spread over the
spores, viruses and worm eggs, resistant to
Many investigators consider this method
the best for the disinfection.
•House hold purification of water
•Disinfection of wells
By Boiling:
Water should be boiled for
5 -10 minutes.
It kills all bacteria, spores,
cysts & ova.
It removes temporary
Taste is altered but is
b. Chemical disinfection
i) Bleaching Powder (CaOCI2)
Bleaching powder is a white amorphous powder.
Produced by action of chlorine on slaked lime.
When freshly made contains 33 % of available chlorine.
It must be stored at dark, cool, dry place in a closed
container that is resistant to corrosion.
In practise one cup (250 g) of laundry bleach is mixed with three
cups (750 ml) of water to make a litre. Three drops of this
solution are added to 1 litre water for disinfection. Contact
period is 30 minutes to 60 minutes.
ii Chlorine Solution
Chlorine solution may be prepared from bleaching powder.
* If 4 kg of bleaching powder with 25 % available chlorine is
mixed with 20 litres of water, it will give a 5% solution of
* This solution should be kept in dark, cool and dry place in
closed container
iii. Chlorine tablets
Available under different trade
name e.g. Halazone
One tablet of 0.5 g is sufficient to
disinfect 20 litres of water. Used in
camps and during travel.
iv. Iodine:
Two drops of 2 % ethanol solution
of iodine is used. A contact period
of 20 - 30 minute is sufficient for 1
litre water.
It is a powerful oxidizing
agent but not recommended
as it alters colours, smell and
taste of water.
 Deodorization - elimination of smack and odour of
water by aeration, usage of oxidants (ozonization,
dioxide of chlorine, large doses of chlorine,
potassium permanganate), filtrating through a layer
of absorbent coal, by introduction in water to
sedimentation of absorbent coal.
 Deironation is carried out by spraying water with
the purpose of aeration in graduation towers. Thus,
bivalent iron is oxydated in iron hydroxide, which
sediments in settling tank, or delays on the filter.
Softening or Removal of hardness
I.Temporary Hardness
Addition of lime
Addition of sodium carbonate
Permutit process
II. Permanent Hardness
Addition of sodium carbonate
Permutit process/ Base exchange process.
It removes temporary hardness by expelling carbon
dioxide and precipitating the insoluble calcium carbonate.
Ca (HCO3)2→ CaCO3 + CO2 + H2O
Addition of Lime:
It removes temporary hardness. Lime absorbs
carbondioxide and precipitates the insoluble calcium carbonate.
Ca (OH)2 + Ca (HCO3)2 →2 CaCO3 + 2H2O
Addition of Sodium Carbonate,
It removes both temporary and permanent hardness.
Na2CO3 + Ca (HCO3)2 → 2NaHCO3 + CaCOs
Na2CO3 + CaSO4 → Na2SO4 + CaCO3
Base Exchange Method
In this method sodium permutit is used, which is a
combination complex of Na, Al and Si (Na2 Al2 Si2OH2O)
Sodium permutit has property of exchanging the sodium cation
for Ca++ and Mg++ ions in water.
Na2 Al Si2O + H2O = Mg++/Ca++
When hard water passed, sodium permutit exchanges
Mg/ Ca and is converted into calcium and magnesium
With time permutit loses effectiveness, it is regenerated
by adding conc. sol of NaCI.
By this process hardness of water is removed to zero.
As zero hardness is corrosive, therefore a part of raw water is
mixed with softened water.
About 97 percent of the water on earth is in the salty oceans.
People have found many ways to desalinate, the process for
removing salt from seawater and brackish water. The
desalination processes used most commonly today are
distillation, reverse osmosis, and electrodialysis. These
processes produce fresh water from salt water.
This is a water purification
Distillation is the oldest
water into fresh water.
Seawater can be distilled by
simply boiling it in a teapot,
and piping the steam into a
cool bottle. The salt water
turns to vapour under the
sun's heat. The vapour rises
until it hits the underside of
the dome or glass, where it
Most modern distillation plants use a process
called multistage flash distillation. This is a type
of the age-old method of boiling and
In flash distillation, preheated seawater flows
into a large chamber in which the pressure is
low. The low pressure causes some of the water
to instantly turn into steam The steam is
condensed into salt-free water. The seawater
passes through several distillation chambers.
Each of the chambers has a lower pressure than
the previous chamber. Often, the final water is
so pure that it is tasteless, and some salt must
be tossed back in to give it flavour
Reverse osmosis is a widely used method for desalting seawater
and brackish water. In normal osmosis, a less concentrated
liquid flows through a membrane into a more concentrated
liquid. Thus, if salt water and fresh water are separated in a
chamber by a special semi-permeable membrane, the fresh
water will flow through the membrane into the salt water.
chiefly to desalt brackish ground water
and water from estuaries, or river
mouths. Electrodialysis is based on the
fact that when salt is dissolved in
water, it breaks up into ions, or
electrically charged particles, of sodium
and chloride. Sodium ions carry a
positive charge, and chloride ions carry
a negative charge.
Other desalting processes are also being
studied. During the 1970's, several plants
experimented with freezing as a method of
desalination. When seawater freezes, the ice
crystals produced are pure water in solid
form. The salt is separated and trapped
between the ice crystals.
0,7-1,5 mg/dm3 of fluoride
is the optimal concentration
of fluoride in water.
Fluoridation is addition of fluoride to public water supplies to
reduce tooth decay.
Fluoride is a compound consisting of the element fluorine and a
metallic element such as sodium (forming sodium fluoride, used
in water supplies) or tin (forming stannous fluoride, used in
Water fluoridation has been recognized as a significant method in
preventing tooth decay since the 1930s.
The maximum protection by fluoridation against tooth decay
occurs when children consume fluoridated water from birth
through age 13.
For hygienic purposes the
examination of water is
generally done under the
following heads:
1. Physical Examination.
2. Chemical Examination.
3. Microscopical
Before water from any 4. Bacteriological
source is declared fit for
human consumption, it is
essential to carry out the
following examination.
Control question:
1. How is water treated?
2. What are the principles of water
chlorination ?