U.S. Air Force Airman Alex McClendon, 633rd Aerospace Medicine Squadron bioenvironmental engineering technician, adds a pH-testing solution to a tap water sample at Langley Air Force Base, Va., June 12, 2015. Bioenvironmental Airmen from the 633rd AMDS bring no less than 10 samples to the laboratory monthly, as to ensure the water is free from coliform bacteria. (U.S. Air Force photo by Airman 1st Class Devin S. Michaels/Released)