This slide presentation outlines the impacts of precautionary assumptions in risk assessment on benefit-cost analyses and standard setting for drinking water. An outline of the presentation includes: the origins and rationale for caution; distinguishing key terms such as "precautionary principle" and "precautionary assumptions"; the role of precaution in risk assessment (quantifying effects), and risk management (setting standards); and, the impact on benefit-cost analyses (BCA). Topics outlined include: a blending of science and policy; precautionary implications for BCA; mandates for realistic BCAs; exposure assessment; dose-response functions; impact of cancer risk assessment assumptions; impact of illustrative uncertainty factors in reference dose estimates; adjusted value of statistical life (VSL) estimates (million 1999 dollars); compounded impacts; key issues and recommendations. Includes tables, figures.