Water Quality Index (WQI) has been calculated for surface drinking water in Kolavai Lake, Chengalpet Taluk, Kancheepuram District, Tamil Nadu, India, at four different sites in the monsoon, post monsoon, summer and pre monsoon seasons. Water quality parameters thirteen were selected as per the BIS guidelines and water quality physico-chemical parameters were estimated following the standard methods and procedures. The lake water of some sites was found to be moderately contaminated. Water Quality Index during the years 2011 and 2012, in general, the water quality showed deterioration. It is felt that some remedial measures are urgently required to optimize the water quality for this region.