[Chlorination of piped water supplies in large cities of China]

151 tap waters in 140 Chinese larger cities were investigated. In North China, under-ground waters were 47 out of 69; in South China, surface waters were 74 out of 82. Disinfection with liquid chlorine was the main treatment process (about 125 tap waters). In general, pollution of the raw waters in the South were higher than that in the North; in the surface waters were higher than that in the under-ground waters. It was the same with the amount of chlorine demand during chlorination. The average amount of chlorine added into the tap waters was 2.12mg/L, their average demand of chlorine was 1.43mg/L, and the average amount of residual chlorine was 0.68mg/L. The amount of chlorine demand during chlorination of the tap waters was markedly affected by the amount of NH+4(N), NO2- (N) or chemical oxygen demand in them, but not affected by the microorganisms in them. No sample of the tap waters contained more than 3/L coliform groups and 100/L bacterial total counts, when their residual chlorine was higher than 0.3mg/L.