Pinellas County, Florida is typical of many major metropolitan water systems, with over 700,000 customers, 2,000 miles of piping and several large water storage facilities. Like many major metropolitan water systems, Pinellas County Department of Environment and Infrastructure (DEI) has seen a decline in water usage over the last decade, both due to active water conservation programs and downturns in the regional economy. This decrease in water usage has increased water age, and coupled with warm southern temperatures, has increased incidences of nitrification in parts of their chlorinated system.

In 2000, Pinellas County DEI embarked on a major upgrade in anticipation of their conversion to chloramines as a secondary disinfectant and installed passive mixing systems in each of their ground-level water storage tanks. Once the chloramine conversion was complete in 2002, DEI found that nitrification was still an issue in some of their storage tanks. To reduce nitrifying bacteria and biofilm growth, DEI performed a chlorine maintenance (or free chlorine burn) each spring in which the secondary disinfectant was switched from chloramines to free chlorine for several weeks. DEI also increased its flushing, averaging roughly 255 million gallons of water per year.

In 2009, Pinellas County DEI experienced its earliest recurrence of nitrification after chlorine maintenance in the beach community at the southern end of the County. Despite the presence of passive mixing systems in their tanks, operators at DEI were aware that mixing conditions were not optimal. One indication: as tanks were drained, operators saw a steady drop of chlorine levels, suggesting that the upper layers of water in the tanks were depleted of disinfectant residual.