In aqueous solutions with pH w7.0 (about the levels found in the filter influent samples), HOCl reacts rapidly with ammonia
to form inorganic chloramines depending on the relative ratio of NH3eN and the chlorine dose applied. In this case, the filter influent samples contained high NH3eN levels (mean value, 0.6 mg/L, see Table S2) and the chlorine dose applied was w4 mg/L (ratio w6.5:1 by weight), thus chloramines rather than free chlorine was the real disinfectant present in this
step. Then, the water was pumped to 6 storage tanks of about 5000 m3, where it was stored up to 24 h. At the exit of the
DWTP, the water was again dosed with sodium hypochlorite (and fluoride) in order to maintain a chlorine residual
concentration of about 0.2e1.0 mg/L through the distribution system (postchlorination and fluorination steps).