Abstract: During 1996~1998,drinking water quality of non-centralized water supply(NCWS)and tap water from deep-well(TWDW) was assessed in terms of physical,chemical,microbiological and toxicological parameters in 10 villages with TWDW and 12 control villages.The results showed that before the improvement,only 10% and 11.4% in total number of bacterial colony and coliform were in keeping with the first grade standard of the Guideline for Implementation the Sanitary Standard for Drinking Water in Rural area respectively.After introduction of TWDW,this rate rose to 45% and 70% respectively,but the non-qualifying rate still remained too high.The assessment results of the sanitary index of water quality(SIWQ)indicated that altogether 81.6% of water samplesmet 4~6 grade water quality requirement for NCWS and 60.0% of TWDW samplesmet 1~3 grade water quality requirement.Judging by physical and chemical indices of the SIWQ(except microbial indices),there were still 18.8% classified as 5~6 grade water,which indicated that the non-microbial properties of deep-well tap water still merits further much attention.Ames tests for all NCWS were all positive,their decreasing intensity:Huai river water and Caoy ang river>pond water>shallow well water.One of the deep-weel tap water sample was also positive.In general,the pollution of deep-well water through water-pipe is of primary sanitation concern.