Currently under investigation at the Langley Research Center in Hampton, Va., is a research test chamber to study and test life support subsystems for long-duration space missions. This system is designed to support four men for a period of 1 year in a near-earth circular orbit with resupply at a 90 day interval. Critical life support subsystems include the recovery of water from urine, waste management, and personal hygiene. Microbiological studies in support of the development and testing of a wick evaporator, water management subsystem are reported. The goal of this program is to produce water meeting the recommended standard of “essential sterility,” that is, no more than a sum total of 10 micro-organisms per ml. Modification of the wick evaporator system to permit the use of heat for sterilization will be described. Microbiological and chemical results obtained during research and development on a bench model and from two units inside the ILSS test chamber are presented. The multidisciplinary approach used in this program and the background philosophy behind water standards for space missions are discussed. The laboratory techniques used for the microbiological examination of samples from the water management system are reviewed.