The elimination of mold should therefore be a priority for school administrators concerned about IAQ and, since mold and other microbes need moisture to grow, any wet area should be considered a hot spot. Water in a school can come from direct sources like a flooded basement or leaky plumbing, or more indirectly from materials that have absorbed water vapor or surfaces where water vapor has condensed. Water from outside is the most obvious source of moisture. Flat roofs that accumulate water and sometimes leak are common in schools and can start a chain of microbial growth on insulation and other materials underneath the roof. This problem can be compounded when water from the roof penetrates an area that serves as a return air plenum, making part of the air pathway itself a microbial amplification source.
Water can also enter a building through leaks around windows, causing damage to walls and carpeting.
Another type of water problem can develop during the construction process. If proper precautions aren't taken, rain can flood the partially constructed structure before the roof or windows are in place, or building materials can be water damaged and installed wet. One school's IAQ problem began when its sprinkler system was directed at the outside air intakes, resulting in microbial growth. Usually, this problem results from overflowing drain pans in the HVAC units, broken water lines or leaky water valves. Plumbing backups can also cause localized flooding and microbial growth on carpeting and walls.