The overall economic, environmental and social costs of water pollution caused by agriculture across OECD countries are likely to exceed billions of dollars annually, although no satisfactory estimate of these costs exists. The economic cost of agricultural water pollution is significant in many countries. Treating water to remove nutrients and pesticides to ensure water supplies meet drinking standards can be substantial for water treatment companies, and ultimately paid for by consumers. Eutrophication of fresh and marine waters can also impose economic costs on ecosystems, recreational and amenity benefits, spiritual values, and recreational and commercial fisheries. Monetary values for the impacts of agriculture on water systems is lacking in the policy debate, with reliance largely on physical measures of water quality. When reliable estimates of economic costs and benefits from agriculture on the environment, including water systems, can be calculated, they can define the scale of different environmental problems for policy makers and direct focus to areas with the greatest potential societal costs.