The critical role groundwater plays as a decentralised source of drinking water for millions of rural and urban families cannot be overstated. According to estimates, it accounts for nearly 80 per cent of the rural domestic water needs and 50 per cent of the urban water needs in India.
 

          Groundwater is generally less susceptible to contamination and pollution when compared to surface water bodies. Also, the natural impurities in rainwater, which replenishes groundwater systems, get removed while infiltrating through the soil strata.

      
         In India, where groundwater is used intensively for irrigation and industrial purposes, a variety of land and water based human activities are causing pollution of this precious resource. Its over-exploitation is causing aquifer contamination in certain instances, while in certain others its unscientific development, with insufficient knowledge of groundwater flow dynamics and geo-hydrochemical processes has led to its mineralization and organic contamination.

       
        The incidences of Fluoride and Arsenic above their permissible levels in the groundwater occur in various Indian states, namely - Andhra Pradesh, Rajasthan, Bihar, Gujarat, Haryana, Karnataka, Madhya Pradesh, Maharashtra, Orissa, Punjab, Rajasthan, Tamil Nadu, Uttar Pradesh and West Bengal, affecting a total of more than 100 districts.

    
         Apart from these toxic pollutants, the groundwater is also facing a threat from unsewered domestic waste that can cause severe groundwater contamination by pathogenic bacteria, nitrate and other pollutants. Non-point pollution caused by fertilisers and pesticides used in agriculture, often dispersed over large areas, is a great threat to fresh groundwater ecosystems. Intensive use of chemical fertilizers in farms and indiscriminate disposal of human and animal waste on land, result in leaching of the residual nitrate causing high nitrate concentrations in groundwater.

     
         Three fourth of the world population lives in developing countries like India, where there is an alarming trend of groundwater pollution due to nitrates. A study conducted in Bulgaria has shown that when groundwater is being tapped in pockets, nitrates from the surrounding soil profile can migrate and accumulate in such pockets and this phenomenon has been observed in soils which are otherwise low in nitrate concentration. Such studies serve as a warning to countries like India of the impending nitrate pollution, where groundwater exploitation is growing at a tremendous rate.

       
          The nitrate concentration In India is above the permissible level of 45 ppm in 11 states, covering 95 districts and two blocks of Delhi. It is known that excess levels can cause methemoglobinemia, or “blue baby” disease in infants. Although nitrate levels that affect infants do not pose a direct threat to older children and adults, they do indicate the possible presence of other more serious residential or agricultural contaminants, such as bacteria or pesticides.       

      
         Possible causes of nitrate contamination of drinking water include cultivation of crops for which high doses of nitrogen fertilisers are applied: e.g. tobacco, vegetables, flowers, etc. It must be emphasised that organic farming does not ensure freedom from nitrate problems. DDT, BHC, Carbamate, Endosulfan etc. are the most common pesticides used in India. In agriculture intensive areas of Punjab, Maharashtra, and Andhra Pradesh, where fertilizer applications are high, there is ample evidence of pollution of groundwaters due to nitrates. Even in semi arid regions of the Deccan plateau, and the arid regions of Rajasthan, where the intensity of agriculture is less, nitrate leaching is freely prevalent.

     
          Another important area is industrial and urban centres, where nitrate pollution of groundwater has been found rampant. This phenomenon has been attributed mainly to dumping of animal manure, organic wastes from industries and sewage on to the soil. In most of the above studies, nitrate concentrations in groundwater exceeded the permissible limit.

Existing Issues in Nitrate Contamination

        There are mainly two issues that govern nitrate contamination in the rural areas. Nitrate pollution can be properly controlled through the appropriate dosage of fertilisers; crop rotation; proper timing of fertilizer application; use of organic manure instead of chemical fertilizers; and safe sewage disposal practices. However, there are no institutional regimes governing fertiliser use and dumping of animal waste.
 

        An appropriate  step towards evolving measures to prevent and cure groundwater quality deterioration is Water Quality Monitoring (WQM). However, there are only few organisations in the country that cover all the essential parameters for WQM. Due to the lack of reliable WQM facilities, the data obtained are not decisive on the water quality status which could be used to facilitate the necessary treatment solutions in a particular area.

Reducing the Severity on Humans

        Before adopting the ‘Best Available Technology Not Entailing Excessive Cost’ (BATNEEC) for decontaminating nitrate-containing drinking water, it is necessary to minimise nitrate leaching from agricultural as well as non-agricultural activities at the source. Any change which may involve conversion from agriculture to non-agricultural use, conversion to grasslands, change in the cropping system or reduction in the fertiliser dose involving a reduction in food production, would not be appropriate in India and other developing countries, where the challenge is to maximise the food production with no increase in the cultivable land.

        In developing countries, the stress will be on maximising the fertiliser use efficiency. However, by adopting the following improved methods of nitrogen fertiliser use, it is possible to minimise nitrate leaching:  
 

        It is the ordinary people who raise the alarm about the poor water quality. In fact civil society / institutions need to be strengthened to respond to water quality problems quickly. This is only possible through better knowledge and information about the nature of groundwater contamination; potential sources of threats to groundwater quality in their region and their degrees of vulnerability; the ill-effects of using contaminated water; and the possible preventive measures.

        The fact, that the cost of pollution is much less than the cost of its treatment need to be understood very well and environmental management projects should be always executed with the total participation of the local bodies and the concerned NGOs to tackle this havoc..q

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