Outbreaks of hepatitis A (HA) attributable to water contamination have been reported; however, the impact of water supply characteristics on the endemic rates of HA has not been quantified. This study did not detect any statistically significant associations between endemic HA rates and water supply characteristics. Because of the sample size, this finding suggests that the total variation of HA rates attributable to water supply characteristics is probably less than 8 per cent of the annual reported cases of HA in the United States.