U.S. Air Force Airman 1st Class Alex McClendon, 633rd Aerospace Medicine Squadron bioenvironmental engineer technician, tests a water sample at Langley Air Force, Va., Jan. 9, 2015. McClendon used phenol red to test the pH levels of the base water supply. In addition to testing pH levels, the 633rd AMDS test ten samples of water per month for bacteria. (U.S. Air Force photo by Airman 1st Class Areca T. Wilson/Released)