A study on Hygiene in long duration space missions was held between 1988-1989 for ESA Long Term Programme Office (1), (2).The impact of Hygiene on station contamination and station layout was reviewed as well as psychological, social and cultural aspects, leading to the conclusion that hygiene is a key habitability issue.Among its main results, the study highlighted the importance of water in both environmental and personal hygiene: the use of water in body hygiene is culturally and socially established. As a consequence, water was found as the main consumable in hygiene functions.Thus, due to the limited water availability in space stations, particular attention was paid to on board water management. Simulation software was developed to demonstrate the relation between hygiene subsystems concepts and water requirements. The software was designed as a tool. Parameters allow to define various mission profiles. Optimistic, realistic and pessimistic scenarios concerning water use are available. Elementary water requirements are user-defined. This tool was used to establish the relevancy of candidate water recycling techniques and water loops.Overall and detailed results from the software are presented in conclusion.