Chemical Characterization of ISS Potable Water Collected in 2017

This paper presents and discusses results from chemical analyses performed on archive potable water samples collected in the U.S. Segment of the International Space Station (ISS) during Expeditions 50-53. The sixth increase in the total organic carbon (TOC) concentration of the water produced by the U.S. water processor assembly (WPA) began during Expedition 50. Despite an initially precipitous climb, the TOC trend reversed several times and levels remained well below the potability limit. There have been five prior instances of organic contaminants breaking through the treatment process into the WPA product water since the system became operational in 2008. Contaminant breakthrough was signaled each time by an increase in TOC measured by the onboard TOC analyzer (TOCA). In all previous instances, the WPA multifiltration beds were replaced and the TOC concentration returned to nominal levels. The archival sample results discussed herein indicate that dimethylsilanediol (DMSD) was the primary compound responsible for the latest increase.