The increasing contamination of groundwater by nitrate, primarily from the widespread use of commercial fertilizers, is an evolving public health concern in agricultural states. Nitrate can undergo endogenous reduction to nitrite, and nitrosation of nitrites can form N-nitroso compounds, which are potent carcinogens. There are few epidemiologic data, and no prospective cohort data, on whether nitrate exposure from drinking water increases the risk of cancer, in particular cancers of the digestive tract, the urinary tract, and non-Hodgkinlymphoma. This study proposes linking the Iowa WomenHealth Study, a prospective cohort study of cancer in women aged 55 to 69 years in 1986, to historical water quality databases available from CHEEC. Average nitrate exposure from drinking water over a 10 to 20 year window will be related to cancer risk, after adjustment for age, dietary nitrate intake, factors which impact endogenous nitrosation (vitamin C and E intake and smoking), and other site-specific confounders.