Assessment of Drinking Water Quality in Delhi City

Assessment of water quality at the treatment plants and consumer ends in Delhi city was undertaken during June to November for two consecutive years 2006 and 2007 to assess the quality as per BIS 10500:1991. Physico-chemical and microbiological quality of treated water from five treatment plants was assessed fortnightly during the survey period. Water samples were also collected from private taps and public hydrants used by consumers from 24 areas across the city from distribution network. These Samples from distribution system were analyzed further for total and faecal coliforms, along with free residual chlorine. It is observed from assessment of treated water quality at treatment plants that essential characteristics such as pH, turbidity, total hardness, chloride, etc. are well within the desired limits as per BIS norms. Free residual chlorine ranged between 1.5 to >2.0 mg/L and no sample was found to contain total or faecal coliform. It is observed that total coliforms are detected in 6.8% of water samples at consumer ends, even though coliforms were not detected in the treated was at treatment plants. Improvement in water quality at consumer ends is observed in year 2007 as compared to 2006 due to remedial actions taken by Delhi Jal board. Chorine less than 0.2 mgll was detected in 13.4% and 0.1 % samples in year 2006 and 2007 respectively. 3.5% of the water samples were found to contain total coliform in 2007, as compared to 10% in 2006. Total coliform counts exceeding 10 were detected in 1.3% samples in 2007 as compared to 4.8 in 2006. Faecal coliforms were detected in only 0.6% samples in 2007, as compared to 4. % in 2006. It is observed that water gets contaminated in distribution network, even if treated adequately at treatment works to render it safe and acceptable. This could be attributed to intermittent mode of water supply, use of inline booster pumps by consumers and leakages in service pipelines. It is desirable that quality of water be adequately safeguarded especially during distribution phase to protect the public health.