DRINKING WATER:-
INTRODUCTION:-
Water is essential for the survival of any form of life. On an average, a human
being consumes about two liters of water every day. Water accounts for about 70
percent of the weight of a human body. Water available is used for drinking,
domestic, agriculture, industrial consumption. Owing to increasing
industrialization on one hand and exploding population on the other, the demands
of water supply have been increasing tremendously.
In our home, water is used for drinking, cooking and washing purposes. Although
there is an enormous quantity of water in the world, the reservoirs of fresh and
quality water are very limited. Human activities are destroying the quality of
water. The quality of clean water supply is of vital significance for the
welfare of mankind.
We know water is an excellent solvent, dissolves a wide variety of compounds.
Natural water, when it flows over or seeps through the surface of the earth,
dissolves various minerals including salts and other substances. Despite these
mineral impurities water from most of the lakes, rivers, springs and wells is
considered fit for drinking and other domestic uses. Water is considered
polluted, when it is contaminated with substances which are harmful and
injurious for human beings and other living things. Polluted water is unfit for
drinking purposes.
Considerable part of the available water is polluted by sewage, industrial
wastes and wide array of synthetic chemicals.
CLASSIFICATION OF WATER POLLUTANTS:-
There are various types of water pollutants which can broadly be classified into
different categories.
1- Oxygen – Demanding Wastes:-
These include domestic and animal sewage, bio – degradable organic compounds and
industrial wastes from food – processing plants, meat packing plants, slaughter
houses, paper and pulp mills, tanneries etc. All these wastes undergo
degradation and decomposition due to which there is a rapid depletion of demand
oxygen. (D.O) from water which is harmful to aquatic animals. Many aquatic
animals can not survive at lower D.O levels in water.
2- Synthetic Organic Compounds:-
These are the man – made materials such as synthetic pesticides, synthetic
detergents, food additives, pharmaceutals, insecticides, paints, fibers,
solvents, plastics etc. These materials are potentially toxic to plants, animals
and humans. They cause offensive colors, odours and tastes in water.
3- Disease – Causing Wastes (Micro Organisms):-
Disease causing wastes include pathogenic micro-organisms which may enter water
along with sewage and other wastes and may cause tremendous damage to public
health. These microbes, comprising mainly of viruses and bacteria can cause
dangerous water- borne diseases such as typhoid, cholera, polio, dysentery,
infections hepatitis in humans. Hence disinfection is the primary step in water
pollution control.
4- Agricultural Water Pollutants:-
In modern agriculture, pesticides, fertilizers and organic wastes (manure) are
essential for producing high yields of crops required for the world’s growing
population. There are over one thousand chemicals compounds that are currently
being used. Some common pesticides used in Pakistan are alderin, DDT, dielderin
etc. When too much of these are accumulated, they become a cause of pollution.
Some inorganic pollutants, comprising of mineral acids, inorganic salts, finely
divided metals, trace elements, cyanides etc, also contaminate water.
QUALITY OF DRINKING WATER:-
Municipal water is mainly used for drinking and for cleaning, washing and other
domestic purposes. The water that is fit for drinking purpose is called potable
water, it should be free from all sorts of pollutants.
Some characteristics of potable water are given as under:
1- It should be colorless, odorless and tasteless.
2- It should be free from germs, bacteria and other pathogenic organisms.
3- It should not contain any toxic dissolved impurity such as heavy metals and
pesticides.
4- It should have a pH in the range of 7 – 8.5.
5- It should be moderately soft. Its hardness should not be above 150 p. p. m
(parts per million).
6- It should not stain clothes.
7- It should be free from corrosive substances.
The municipal water supplied for drinking and other domestic uses, has to be
treated before the supply for the domestic purpose. The raw or impure water
obtained from sources such as rivers, lakes, wells and tube wells, etc.
Should undergo treatment by various steps tp make it fit such as:
1- Aeration.
2- Settling.
3- Coagulation.
4- Filtrations.
5- Chlorination (for sterilization to destroy bacteria and pathogenic
organisms).