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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.

For long duration space flights, wastewater from humidity condensate, urine, and used hygiene water will be recycled to provide an adequate supply of potable quality water for the crew. Due to the diverse nature and multiple sources of contaminants entering the recycling system, it is a challenge to maintain the quality of product water such that no adverse health effects occur. NASA Johnson Space Center in cooperation with the Committee on Toxicology of the National Research Council (NRCCOT) has developed a science-based approach, taking into consideration space flight induced factors, to derive Spacecraft Water Exposure Guidelines (SWEG) for 1, 10, 100, 1000 days of consumption. This paper will discuss the ongoing process of setting SWEGs, how candidate chemicals were chosen for risk assessment, and how various toxicological data are collected and interpreted. Our goal is to help environmental engineers understand how the SWEGs they use for hardware design are developed.