Distribution system nitrification is a recurring phenomenon that many monochloramine-utilizing utilities battle in the warm summer months.  Monochloramine is a persistent and effective disinfectant that is especially valuable in preventing disinfection by-product formation.  However, the natural degradation of monochloramine as water ages and temperatures increase liberates free ammonia into the distribution system.  Free ammonia sets off a cascade of nitrifying bacteria growth that increases the levels of nitrite and nitrate in distribution systems (nitrite MCL is 1 mg/l and nitrate MCL is 10 mg/l). Importantly, while nitrite and nitrate levels can be of concern, their presence may also indicate an overall declining level of distribution system disinfectant that can, in turn, permit other types of more pernicious bacteria to flourish.