Cancer mortality and type of water source: findings from a study in the UK.

The age-adjusted, sex-specific mortality rates from certain cancers of the digestive system were analysed by type of water source supplied to 238 urban areas in England, Wales and Scotland using weighted multiple regression. Of the types of water source, the per cent supplied from upland rivers best described the pattern in cancer mortality for each cancer site and each sex. After adjustment was made for a number of socioeconomic factors, the regression coefficient for the percentage of upland river supply remained statistically significant only for female stomach cancer and female intestinal cancer. The association with intestinal cancer could equally well be explained by some other factor with a strong north-west/south-east geographical distribution. The association found for female stomach cancer could not be accounted for by a geographical trend, but suggests a small effect, equivalent to a relative risk of only 1.11. This is an unexpected finding and must be considered a hypothesis, to be tested further by studies conducted by other researchers, in different locations, preferably on individuals.