The overuse of nitrogen fertilizer primarily by large scale agriculture has polluted streams and lakes, and, in turn, coastal waters around the world. One consequence is the contamination of drinking water sources relied on by millions of consumers. Nitrogen is toxic to human health. Clean Water Act regulations require that drinking water supplied by public utilities contain less than 10 ppm of nitrogen. Water utilities in regions with high nitrogen concentrations must install expensive treatment systems to meet the nitrogen limit. This necessity creates an externality from agricultural production. This poster seeks to estimate the cost to utilities of abating nitrogen coming from agriculture.