Airman 1st Class Spencer Hearn, 28th Medical Operations Squadron bioenvironmental engineer technician, uses Colilert testing agent to test water on Ellsworth Air Force Base, S.D., Nov. 30, 2011. Hearn tested water in the base swimming pool to determine if any E.coli bacteria or coliforms were present, after thorough testing the results came back negative for these bacteria. (U.S. Air Force photo by Airman Alystria Maurer/Released)