What are the source of water supply?

there are three main sources of watter :

1- Rain

2- Surface water : Oceans, Rivers and streams , tanks , ponds & lakes

3- ground water : shallow wells, Deep wells , Springs

1. Rain

Rain is the prime source of all water. A part of the rain water sinks into the ground to form ground water; part of it evaporates back into atmosphere, and some runs off to form streams and rivers which flow ultimately into the sea.

Some of the water in the soil is taken up by the plants and is evaporated in turn by the leaves. These events are spoken of as "water cycle".

Characteristics of rain water:

Rain water is the purest water in nature. Physically, it is clear, bright and sparkling. Chemically, it is very soft water containing only traces of dissolved solids (0.0005 percent).

Being soft, it has a corrosive action on lead pipes. Bacteriologically, rain water from clean districts is free from pathogenic agents.

Impurities of rain water:

Rain water tends to become impure as it passes through the atmosphere. It picks up suspended impurities from the atmosphere such as dust, soot and microorganisms and gases such as carbon dioxide, nitrogen, oxygen and ammonia.

Gaseous sulphur and nitrogen oxides are emitted from power plants that use fossil fuels. These gases react with atmospheric water, forming dilute solution of sulphuric and nitric acid. The precipitation of these acids (acid rain) has begun to have serious impacts on surface water quality and on plants etc..

2. Surface water

Surface water originates from rain water. It is the main source of water supply in many areas. Examples of surface water include rivers, tanks, lakes, man-made reservoirs and sea water.

Surface water is prone to contamination from human and animal sources. As such it is never safe for human consumption unless subjected to sanitary protection and purification before use.

Characteristics of surface water:

Surface water picks up the characteristics of the surface over which it passes. If water flows across a parking lot, gasoline, oil, and other contaminants may be carried by or dissolved into the water.

Water may pick up fertilizers, road salts, radioactivity, and biological contaminant from farms, as well as countless other biological, physical, and chemical pollutants.


Many rivers furnish a dependable supply of water. The chief drawback of river water is that it is always grossly polluted and is quite unfit for drinking without treatment.

Characteristics of river water:

River water is turbid during rainy season; it may be clear in other seasons. Clarity of water is no guarantee that the river water is safe for drinking. River water contains dissolved and suspended impurities of all kinds. The bacterial count, including the human intestinal organisms may be very high.

Impurities of river water:

The impurities of river water are derived from surface washings, sewage and sullage water, industrial and trade wastes, and drainage from agricultural areas.

Self-purification of river water:

Certain amount of self-purification occur in river water by natural forces of purification such as dilution, sedimentation, aeration, oxidation, sunlight, plant and animal life ,but these agencies are not sufficient to render the water potable. River water needs purification before it can be used for drinking purposes.

Sea water:

Though this source is plentiful, it has great many limitations. It contains 3.5 percent of salts in solution. Desalting and demineralization process involves heavy expenditure. It adopted in places where sea water is the only source available.

3. Ground water

Rain water percolating into ground constitutes ground water. Water used by humans comes mainly from land. It is now realised that there is a limit to ground water in the world.

Ground water is the cheapest and most practical means of providing water to small communities. Ground water is superior to surface water, because the ground itself provides an effective filtering medium.

The advantages of ground water are:

(1) It is likely to be free from

pathogenic agents;

(2) It usually requires no treatment;

(3) The supply is likely to be certain

even during dry season;

(4) It is less subject to contamination

than surface water.

The disadvantages of ground water are:

(1) It is high in mineral content, e.g.,

salts of calcium and magnesium which increase the water hard;

(2) It requires pumping or some arrangement to lift the water.


Traditionally wells are an important source of water supply. Even today, they are an important source of water supply in many communities. Technically, wells are of two kinds-shallow and deep.

(1) Shallow wells:

shallow wells tap subsoil water i.e. the water from above the first impervious layer in the ground. They provide limited quantities of water, and the water is easy to be polluted unless care is taken in well construction.

(2) Deep wells:

A deep well is one which taps water from the water-bearing stratum below the first impervious layer in the ground. Deep wells are usually machine-dug and may be several hundred meters deep. Deep wells furnish the safest water, and are often the most satisfactory sources of water supply.


When ground water comes to the surface and flows freely under natural pressure, it is called a "spring". Springs may be of two types------shallow springs and deep springs. Shallow springs dry up quickly during summer months, whereas deep springs do not show seasonal fluctuations in the flow of water.

In some geographic areas, springs constitute an important source of water. Springs are simpler to exploit, as no pumping is needed to bring the water to the surface. Springs are exposed to contamination.