Ground water is the rain water which percolates to the ground. Water used by humans comes mainly from land. It is now realized that there is a limit to ground water in the world. We should withdraw only quantities of water that can be renewed.
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.
|Fig 2: Shallow and Deep Wells
The advantages of ground water are
- Free from pathogenic agents
- Do not require any treatment
- Supply is likely to be certain during all seasons
- Less subject to contamination than surface water.
The disadvantages of ground water are
- High in mineral content rendering it hard.
- Requires pumping or some arrangement to lift water
Wells: Traditionally wells are an important source of water supply and even today it is true in many communities. Technically wells are of two kinds shallow and deep.
- Shallow wells: Shallow wells tap subsoil water i.e. the water from above the first impervious layer-in the ground. They yield limited quantities of water and it is most liable to pollution unless care is taken in well construction,
- Deep wells: A deep well is one which draws water from the water bearing stratum below the first impervious layer in the ground (Fig 2). Deep wells are usually machine-dug and may be several hundred meters in depth. Deep wells provide the safest water and are often the most satisfactory source of water supply.
Most of the wells in India are of the shallow type. Generally shallow wells are liable to pollution from neighbouring sources of contamination such as latrines, urinals, drains, cesspools, soakage pits and collections of manure. Shallow wells are therefore a health hazard to the community if they are not made sanitary. A deep well can also become a health hazard if kept open, or poorly constructed and not protected against contamination.
Wells can also be classified according to the method of construction as ‘dug well’ and ‘tube well’. Dug wells are the commonest type found in India. Two types of dug wells exist in rural areas: (a) the unlined katcha well and (b) the masonry or pucca well. The katcha well is a hole dug into the water-bearing stratum. The pucca well is an open well built of bricks or stones. Step wells are a kind of pucca wells having steps inside to facilitate people to descend in and draw water. This is highly susceptible for contamination as water comes in direct contact with people.
Fig 2: Step Well
Improvement of dug wells: The unlined katcha wells may be made sanitary by deepening the bottom, installing a hand pump with screen, filling the well with coarse sand up to the water level and with clay above that level. When the material used for filling is completely consolidated a platform and drainage may be constructed.
Masonry well improvement consists of
- making the upper 10 feet or more of the lining water tight,
- raising the lining one foot above the ground
- providing a RCC slab cover at the top
- installing hand pumps for lifting the water
Sanitary well: A sanitary well is one which is properly located, well constructed, protected against contamination with a view to supply of safe water (Fig).
Tube Wells : Source of drinking water in many parts of India, yield bacteriologically safe water and are cheap compared to other sources. Shallow tube wells or driven wells have become the largest individual source of water supply to the rural community. The area within 15 m of the tube well should be kept free from pollution with liquid and solid wastes.
Springs: When ground water comes to the surface and flows freely under natural pressure it is called a "spring" which may be shallow or deep. Shallow springs dry up quickly during summer months whereas deep springs do not show seasonal fluctuations in the flow of water. Springs are exposed to contamination unless protected by well built structures to safeguard water quality.