This paper identifies information that may be important in determining the benefits of preventing toxic water contamination (or equivalently cost of nonaction) when a given toxification occurs. It attempts to identify information and behavior issues that need to be considered when we estimate benefits and weigh them against the costs of removing toxins. This paper also provides “scenarios” for three toxic pollutants that are found in water bodies. We make use of two alternatives--one for developing countries and the other for developed countries--to demonstrate, with specific examples of arsenic, mercury and Atrazine, how benefit estimates and control policies vary with different assumptions concerning behavior/information and type of chemical contamination. A comparison with EU evaluation experience is also carried out.