75%–80% of water pollution by volume is caused by domestic sewage. The total waste water generated from domestic sources in class I towns is 16.27 billion litres and only 25% of this is treated. A survey of 241 class II towns in 17 states in India undertaken by the CPCB indicates that, on an average, 90% of the water supplied is polluted. Only 1.6% of the total ‘polluted’ waste water is treated (CPCB 1990). The increase in treatment
capacities have not shown a commensurate increase as the share of waste water which is untreated and disposed into our surface water has increased from 61% in 1978/79 to 76% in 1994/95 (CPCB 2000).