Uranium is widespread in nature and has been identified in many different minerals. It exists in several chemical oxidation states. Although natural uranium is a weakly radioactive substance, the principal health effects associated with natural uranium are due to its chemical toxicity. The maximum acceptable concentration is established based on the chemical toxicity of uranium, and the focus of this document is limited to uranium's chemical properties. This guideline technical document reviews and assesses all identified health risks associated with natural uranium in drinking water.