The possible association between the risk of rectal cancer and hardness lev
els in drinking water from municipal supplies was investigated in a matched
case control study in Taiwan. All eligible rectal cancer deaths (986 cases
) of Taiwan residents from 1990 through 1994 were compared with deaths from
other causes (986 controls), and the hardness levels of the drinking water
used by these residents were determined Data on water hardness throughout
Taiwan were collected from Taiwan Water Supply Corporation (TWSC). The cont
rol group consisted of people who died from other causes and the controls w
ere pair matched to the cases by sex, year of birth, and year of death. The
results show a significant negative relationship between drinking water ha
rdness and rectal cancer mortality. Odds ratio and 95% confidence intervals
were 1.24 (1.01-1.55) and 1.38 (1.10-1.73), respectively, for exposure to
moderately hard water and soft water compared with the use of hard water. T
rend analyses showed an increasing odds ratio for rectal cancer with decrea
sing levels of hardness in drinking water. This is an important finding for
the Taiwan water industry and human health. (C) 1999 Academic Press.