Astronauts working in space for extended periods of time will be in a closed environment where both air and water are recycled. As the lengths of missions increase, the astronauts are likely to be at greater risk for viral infection by consumption of recycled water and air. In order to minimize the risk of infection and assure mission success, indicators of the viral quality of recycled water and air will have to be determined. The indicators chosen will depend upon many factors arising from the fields of engineering, public health, virology, and infectious disease. Moreover, selection of viral indicators must address the unavoidable mixing of recycled air and water and the pathogens they contain. This paper is a discussion defining viral quality indicators for potable recycled water and air that reflect the behavior of viruses in a closed, multimedia, space environment The applicability of indicators currently used on earth are considered for use in space. Several viral indicators are proposed for use in monitoring the risks anticipated, and the idea of indicator seeding at various points in the closed environment is presented.