In their Policy Forum (“Nutrient imbalances in agricultural development,” 19 June, p. [1519][1]), P. M. Vitousek et al. propose a promising idea: Compare solutions to nutrient challenges among countries and regions. However, policies to control nonpoint pollution are not so easy to design. The United States and the European Union are mentioned as examples of places that have reduced nutrient imbalances, yet pollution remains very high in their water. European regulations include the 1991 Urban Wastewater Directive, with investments above 100 billion euros. The huge investments of the Wastewater Directive should have reduced pollution, but the European data ([ 1 ][2]) for the past 15 years on nitrate concentration indicate only a slight reduction in rivers and a 50% increase in pollutant levels in aquifers. The data from the Organisation for Economic Cooperation and Development ([ 2 ][3]) also found that most major European rivers show no abatement of nitrates and some have even grown worse. The Nitrates Directive of 1991 also sought to reduce pollution. The Nitrates Directive only applies to cultivation over aquifers declared officially polluted, not to cultivation over whole basins or very polluting crops that do not receive subsidies (such as greenhouses). The achievements of this Directive are questionable ([ 3 ][4]). Nonpoint pollution is a common pool “resource” (or public bad) where economic instruments such as taxes and subsidies fail ([ 3 ][4]). Policy-makers must recognize that pollution abatement is impossible without farmers' voluntary cooperation and active support. This is also the message of this year's Nobel prize in economics. 1. [↵][5] European Environment Agency (EEA), Core Set of Indicators N° 020, Nutrients in Freshwater (EEA, Copenhagen, 2009). 2. [↵][6] Organisation for Economic Co-operation and Development, OECD Environmental Data Compendium 2006 (OECD, Paris, 2007). 3. [↵][7] 1. J. Albiac, 2. A. Dinar 1. J. Albiac 2. et al ., in The Management of Water Quality and Irrigation Technologies, J. Albiac, A. Dinar , Eds. (Earthscan, London, 2009), pp. 61–81. [1]: /lookup/doi/10.1126/science.1170261 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 View reference 1 in text [6]: #xref-ref-2-1 View reference 2 in text [7]: #xref-ref-3-1 View reference 3 in text