Collected fifteen water samples from different sources at different locality of Saharsa area during Feb. 2013. Studied the physico-chemical behaviour of water. Different physical-chemical parameter. pH, EC, alkalinity, TDS, turbidity, total hardness and content of fluorid, sulphate chloride were studied and compared with the standard values prescribed by WHO and APHA. In this analysis, it was observed that the water was not safe for drinking purpose and not suitable for domestic use. The people of this region suffer from severe water pollution, which is a threat to human health and survival of aquatic life. The present investigation revealed that the some of the water sample of Kosi Project are not suitable for domestic use and they need proper treatment before use.