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One of the key issues in achieving water sustainability is the pollution of water resources. Pollution of water resources, particularly the surface water exacerbates water constraints and shortages. Majority of rivers, lakes and seasonal rivulets in the country are today contaminated with the discharge of sewage and effluents.  While the groundwater is largely pure, the leaching of contaminants as pesticide residue and heavy metals is increasingly threatening underground resource too.

Significant progress has been made with regard to availability of appropriate technology to treat the sewage before it is discharged into the surface water. The standards that prescribe the level of treatment before the sewage is discharged into a water body are also in place. In spite of all these, the surface water bodies remain polluted. The river Yamuna is an example of all efforts to improve the quality of wastewater that went waste.

The fault lies in adopting standards that do not take into account the total load of a pollutant into the water body. The standard for Bio-chemical Oxygen Demand, which represents the extent of organic pollution in a water body, is fixed at 30mg/l in the country. This means any industry or infrastructure project or municipality has to treat the sewage or effluent to a level of 30mg/l prior to discharging the same to a water body. A water body like a river does not drain a single source of sewage but hundreds of sources. Even if each source of sewage, say every residential colony discharges the sewage in compliance with regulatory standards of 30 mg/l, the cumulative effect of this is responsible for the current state of affairs of rivers.

Therefore, the standards in the developed countries are being revised and are now being based on the Total Maximum Daily Load calculations rather than a source based limit as not a fixed value but a calculated figure based on (1) sum of the allowable loads of each pollutant from all sources (2) variations in flow and (3) a margin of safety to ensure that the water body can be used for its designated purpose.