On the International Space Station (ISS), atmospheric humidity condensate and other waste waters will be recycled and treated to produce potable water for use by the crews. Space station requirements include an on-orbit capability for real-time monitoring of key water quality parameters, such as total organic carbon, total inorganic carbon, total carbon, pH, and conductivity, to ensure that crew health is protected for consumption of reclaimed water. The Crew Health Care System for ISS includes a total organic carbon (TOC) analyzer that is currently being designed to meet this requirement. As part of the effort, a spacecraft TOC analyzer was developed to demonstrate the technology in microgravity and mitigate risks associated with its use on station. This analyzer was successfully tested on Shuttle during the STS-81 mission as a risk mitigation experiment. A total of six ground-prepared test samples and two Mir potable water samples were analyzed in flight during the 10-day mission. Duplicate test samples were analyzed on the ground concurrent with on-orbit analyses. Archived Mir water samples were returned and analyzed for comparison to in-flight results. Analytical performance of the analyzer during STS-81 was very good. All test sample results except for a few pH values, were within the prescribed analytical acceptance limits for the experiment. The on-orbit and postflight analytical results for Mir water samples were also in good agreement. Postflight inspection of the analyzer revealed that some design changes would be needed before additional flight testing.