The drinking water distribution system of Cremona, in the north of Italy, was monitored for 6 years (2006–2011) analyzing chlorine dioxide, chlorite, and chlorate concentrations. The software Epanet 2.0 (USEPA) was applied to the distribution system. The mixing zone of the water coming from the two drinking water treatment plants, respectively located to the west and east of the city, was estimated using the software. Propagation of chlorine dioxide, chlorite, and chlorate was simulated with the software. Measured and simulated results were compared. The results of the distribution system monitoring showed a high chlorine dioxide consumption, since residual chlorine concentration was always below 0.12 mg L−1. Chlorite concentration was over 700 μg L−1 for 12–16% of results in the first 2 years, for 48% of results in 2008, and for 1–8% of results from 2009 to 2011. In particular, chlorite exceeded 700 μg L−1 at points of the network more distant from the treatment plants. Conversely, chlorate concentration was always below 200 μg L−1. The mixing zone of the water in the distribution system was determined, and the comparison between measured and simulated concentrations showed the usefulness of the model for predicting disinfectant and by-product propagation in the distribution system.

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