NASA maintains an active interest in the environmental conditions associated with living and working in spacecraft and identifying hazards that might adversely affect the health and well-being of crew members. Despite major engineering advances in controlling the spacecraft environment, some water and air contamination is inevitable. Several hundred chemical species are likely to be found in the closed environment of the spacecraft, and as the frequency, complexity, and duration of human space flight increase, identifying and understanding significant health hazards will become more complicated and more critical for the success of the missions. To protect space crews from contaminants in potable and hygiene water, NASA requested that the National Research Council NRC provide guidance on how to develop water exposure guidelines and subsequently review NASA’s development of the exposure guidelines for specific chemicals. This book presents spacecraft water exposure guidelines (SWEGs) for antimony, benzene, ethylene glycol, methanol, methyl ethyl ketone, and propylene glycol.