Of US water systems that chloraminate, an estimated two thirds experie
nce some degree of nitrification in the distribution system. Measures
utilities use to control nitrification were investigated through field
sampling, evaluation of utility data, laboratory tests, and case stud
ies of systems that have evaluated or attempted to control nitrificati
on episodes. Effective control methods included instituting periodic b
reakpoint chlorination, reducing the available ammonia concentration,
increasing chloramine residuals, cleaning the distribution system, and
decreasing system detention time. Some control methods were superior
for controlling a specific nitrification episode, whereas others showe
d more promise for reducing the long-term potential for nitrification
occurrence. According to the authors, the most important steps utiliti
es can take to control nitrification are to thoroughly understand thei
r systems' chloramine chemistry and to establish an effective monitori
ng strategy.