The possible association between the risk of pancreatic cancer mortality and hardness levels in drinking water from municipal supplies was investigated in a matched case-control study in Taiwan. All eligible pancreatic cancer deaths (883 cases) of Taiwan residents from 1990 through 1994 were compared with deaths from other causes (883 controls), and the hardness levels of the drinking water used by these residents were determined. Data on water hardness throughout Taiwan was collected from Taiwan Water Supply Corporation (TWSC). The control group consisted of people who died from other causes and were pair matched to the cancer cases by sex, year of birth, and year of death. The results show that there is a 39 % excess risk of mortality from pancreatic cancer in relation to the use of soft water. Trend analyses showed an increasing odds ratio for pancreatic cancer with decreasing levels of hardness in drinking water. This is an important finding for the Taiwan water industry and human health.