POtable water stOrage tanks are a necessary part of water distribution systems, providing pressure and enough supply for daily and emergency use. but awwa estimates 65 percent of Us storage tanksthat's more than 200,000 tanks-have water quality problems. these problems-common in chlorine and chloramine systems, warm or cold climates-range from temperature stratification, stagnation, dead zones, and short-circuiting to biofilm buildup, loss of residual, nitrification events, and, in northern climates, ice damage.Chlorine systems commonly experience loss of residual and rapid bacteria growth,