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Results of isotope investigations of atmospheric condensate and potable water supplied from Earth confirmed the fractionating of hydrogen and oxygen stable isotopes in the organism of ISS crewmembers. Samples of ISS atmospheric condensate were characterized by altered concentrations of 18O2 and deuterium. Atmospheric deuterium quantities varied in the interval of -67 to 79 +/- 3 ppm, whereas water deuterium made up -85 +/- 3 ppm as compared with SMOW. Atmospheric condensate consists of water vapor transpired and perspired by humans. In addition, cells of crews' red blood were also found to contain increased concentrations of deuterium as compared with the deuterium content of potable water. Results of isotopes measurements in urine, blood, saliva and potable water in a chamber experiment also evidenced in favour of the body fractionating of the stable isotopes of hydrogen and oxygen.

Interplanetary missions, including to Mars, will put crews into severe radiation conditions. Search for methods of reducing the risk of radiation-induced cancer is of the top priority in preparation for the mission to Mars. One of the options is designing life support systems that will generate water with low content of the stable hydrogen isotope (deuterium) to be consumed by crewmembers. Preliminary investigations have shown that a decrease of the deuterium fraction by 65% does impart to water certain anti-cancer properties. Therefore, drinking deuterium-free water has the potential to reduce the risk of cancer consequent to the extreme radiation exposure of the Martian crew.

The methods of deuterium-free water, as applied to the conditions of long-term space expeditions have been discussed. It is shown that with the use of the method of electrolysis of distilled water or urine condensate followed by the catalytic or high-temperature synthesis one can obtained water with four-fold decrease in deuterium concentration. In order to reduce the energy expenditure it is necessary to use the existing routine technologies of water and oxygen regeneration or the versions with applying the fuel cells in which hydrogen and oxygen resulting from electrolysis would generate the electrical power with simultaneous isolation of deuterium-free water.

Various chemicals were assayed as possible urine conservers to the used in space water reclamation systems. With respect to the antimicrobial activity and the quality of reclaimed water formalin at a concentration of 0.1% was selected as the best conserver. The reagent ensures urine preservation for 3 months.

The paper discusses possible application of the method of measuring the total content of organic carbon to evaluate the quality or reclaimed water. The paper gives data on the content of organic carbon, ratio of chemical consumption of oxygen and carbon in the atmospheric condensate, urine, condensate of urine low-temperature evaporation and portable water reclaimed from these sources.