A survey of dietary nitrate in well-water users.

The hypothesis that high nitrate ingestion may increase the risk of stomach cancer has led to concern over rising levels of nitrate in drinking water, but with little consideration as to whether nitrate from water makes a major contribution to total nitrate intake. In order to investigate the relative importance of water and food as sources of nitrate, 404 adult well-water users completed a diet diary over a 48-hour period and provided a 24-hour urine specimen and a sample of their drinking water. Where the waterborne nitrate level is less than 50 mg/I, as recommended by the World Health Organization (WHO), 30% of ingested nitrate is from water. As the well-water nitrate concentration rises the contribution of water to daily intake increases; at levels between 50 and 100 mg/I, on average, nearly 70% of daily intake is from water, and above 100 mg/I over 80% of daily intake is waterborne. Thus it is only at levels above those currently recommended by the WHO that waterborne nitrate appears to be the major contributor to total nitrate intake.