Change in drinking water quality from source to point-of-use and storage: a case study from Guwahati, India.

To ascertain the quality of drinking water being supplied and maintained at Guwahati, the study was conducted on the status of water supply in city through surveillance of drinking water quality for consecutive 7 days at various treatment stages, distribution network and consumer ends. The performance of five water treatment plants (WTPs), viz. Panbazar WTP, Satpukhuri WTP, Kamakhya WTP, PHED WTP and Hegrabari WTP were assessed for summer, piost-post-monsoon and winter seasons. No significant change in raw water quality was observed on day-to-day basis. Residual chlorine was found in the range of nil to 0.2 mg/L in the treated water. During post-monsoon, winter, and summer seasons the thermotolerent TC and FC counts ranged between Nil to 168 CFU/100 ml and Nil to 84 CFU/100 ml; Nil to 3356 CFU/100 ml and Nil to 152 CFU/100 ml; and Nil to 960 CFU/100 ml and Nil to 108 CFU/100 ml respectively. There was variation in bacterial counts among the different service reservoirs and consumer ends, which may be attributed to the general management practices for maintenance of service reservoirs and the possibility of enroute contamination. Evaluation of the raw water quality indicate that the water is suitable for drinking after conventional treatment followed by disinfection. The finished water quality meets the level of standards described as per Bureau of Indian Standard specifications (BIS:10500 1991) for potability in terms of its physico-chemical characteristics.