Two outbreaks of intestinal infectious disease occurred due to contaminations of Two-time pressure water supply at Hai-zhou and Tai-ping districts in 1985 and 1986. There were 659 cases, the incidence rate was 55%. The cause of contamination was that the underground water storage tanks were contaminated by domestic sewage, which back-flowed into the tanks through an overflow pipe, connecting the tank with observation well of the sewage system.
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