Several studies have shown positive associations between diuretic beverage consumption and breast cancer risk (van der Brandt, 1995). Water consumption has been linked to reduced breast cancer risk in a pilot case–control study (Stookey et al. 1997). The study showed that plain water consumption (versus not drinking plain water) was associated with a 4.7 times reduction in risk of breast cancer. The main aim of the present study is to extend the work of the previous study and further investigate the hypothesis that water intake is inversely related to breast cancer risk.