The reduction of organics at Watchgate meant that the amount of chlorine consumed was substantially reduced, but to achieve the disinfection requirements concentrations on the outlet free chlorine concentration of 0.4 mg/l. Reducing the organics entering the distribution system has had a major impact on chlorine concentrations in the system. Chlorine decays slowly in the larger mains and faster in the small mains where it more readily interacts with material at the pipe wall. Historically, all the free chlorine was consumed on its passage down the Haweswater aqueduct, and further secondary dosing was required as it passed into the distribution network. As a result of the reduction in organics, residual chlorine concentrations rose on average by 100 % in the Watchgate system and nearly 200 % in the Oswestry supply (see Table ). Much higher increases were seen in specific zones at the end of the distribution system. What is clear from the chlorine distribution (see Figure ) the distribution of chlorine has also undergone a marked change indicating that chlorine is penetrating much further into the system without substantial loss.