Water quality standards have been completed for space vehicles and habitats for ingestion periods from 1 day to 1000 days. These standards are called spacecraft water exposure guidelines (SWEGs). The National Research Council Committee on Toxicology has worked with the Toxicology Group at the National Aeronautics and Space Administration (NASA) to set and document these standards. Prior to SWEG development, the practice of NASA was to apply the United States Environmental Protection Agency (USEPA) maximum contaminant levels (MCLs) in the interpretation of any potential health effects from water pollutants. This practice had the potential to result in erroneous conclusions because MCLs are intended for lifetime exposures and are set to protect a much more diverse population than is present in the astronaut corps. However, for certain pollutants it was recognized that the stresses of spaceflight may make astronauts more susceptible to adverse effects. NASA also needed shorter-term standards to assist in the creation of flight rules and for management of contingencies that involve off-nominal water pollution. Our goal for this paper is to familiarize the engineering community with the methods used to establish SWEGs and to show how SWEGs can be applied in spacecraft design.