Chloramines are widely used to maintain a disinfectant residual in water distribution systems. However, chloraminated distribution systems can promote the growth of nitrifying bacteria, an undesirable condition known as nitrification. Many chloraminated systems minimize the potential for nitrification by converting from chloramines to free chlorine on a periodic basis. The concept behind this switch is that free chlorine will oxidize any ammonia present in the distribution system, thus removing the food source for nitrifying bacteria, and will reduce the number of nitrifying bacteria.

However, research has never determined how effective this practice is and what other water quality changes occur from the temporary switch to chlorine. This research documents the effectiveness of free chlorine for the control of nitrifying bacteria, evaluates the effect of pipe materials on nitrifying bacteria, and determines how DPBs change as a result of the switch to free chlorine.

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