Many people still depend on underground sources of drinking water. Untreated groundwater is often much cleaner and purer than any surface water. However, even groundwater’s are now threatened with pollution from seepage pits, refuse dumps, septic tanks, barnyard manures, transport acci­dents, etc., and with diverse agricultural, chemical or biological pollutants. One major threat arises from effluents that are discharged on the ground so as to prevent pollution in rivers and streams. Other important sources of pollu­tion of groundwaters include sewage and soluble salts. Groundwater pollution control requires accurate information on the dis­tance between the aquifer and the ground surface on the volume of the groundwater body, and on the nature of the underlying stratum.

Knowledge of the physiochemical and biological properties of the pollutants is also necessary for controlling pollution. For groundwater control, observation pits dug at appropriate points are desirable and through these pits, samples of underground water can be pumped from different depths. Though the common belief is that most groundwaters are free from microbes and are safe for drinking, recent researches have demonstrated the presence of viruses, enteroviruses, Staphylococcus aureus, Klebsiella pneumoniae, E.

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coli and others in many well waters and underground waters (Allen, 1981). Groundwater is also sometimes responsible for outbreaks of waterborne diseases. This happens not only in developing countries but also in advanced countries. In the USA, many waterborne outbreaks of disease have occurred in community and non-community water systems and in groundwa­ter systems in the period 1970-78 (see Craun, 1981). In these outbreaks, Giardia lamblia was the most commonly recorded pathogen.

In India, several episodes of cholera, dracontiasis, giardiasis, hepatitis, shigellosis, jaundice, etc., have occurred from time to time and in most of these either groundwater or surface water were the vehicles of disease transmission. It is generally believed that background monitoring systems can be used to assess the impact of human activities on groundwater quality but this belief is a misconception since many years may elapse in some cases before a change in groundwater quality is observed. Once degradation of the subsur­face regime has occurred, it is very difficult or even impossible to remedy. A potentially significant source of groundwater pollution is blasting, e.

g., in coal mines. Another very important source related to oil shale mining and processing is spent shale. In the industrial areas of Punjab, e.

g., Ludhiana, Ambala, etc., where bicycles and woollen garments are manufactured, abnormally high concentra­tions of nickel, iron, chromium, copper and cyanide have been detected from groundwater samples (Handa, 1978). Fairly high concentrations of the same chemicals occur in the waste effluents of the bicycle industry and this may be responsible for increasing pollution of groundwater in shallow unconfined aquifers in north western India.

An extensive study of urban water supply systems in 75 developing countries was carried out by Dietrich and Henderson (1963). It showed that less than 10 per cent of the total population and about 30 per cent of the urban population were supplied with piped water. Even in these cases, the technical and health standards applicable to water treatment were rather primitive and inadequate and there was no effective supervision of water quality.

In many developing countries, garbage collections are still inadequate and indiscrimi­nate discharges of domestic wastes and sewage into rivers and streams pollute the waters heavily. The problem becomes more serious during summer because of decreased rates of flow in rivers or because of diversion of streams for irrigation.