International Space Station includes a Joint Airlock in the U. S. on-orbit segment to support U. S. and Russian extravehicular activity (EVA). In this plan, the U. S. Extravehicular Mobility Unit (EMU) and the Russian Orlan-M spacesuit system share a common vehicle water coolant loop. Since the two spacesuit systems use different biocide additives and contain different non-metallic materials in their respective cooling water loops, steps are being taken to insure that no deleterious effects occur due to the mixing of Orlan-M and EMU coolant water. This paper describes the activities of the Russian and U.S. International Space Station and EVA teams to understand the implications of using both countries' EVA systems in such a deeply interconnected manner. The paper discusses a current U.S. test program and Russian analyses, and presents results to-date in an ongoing issue.