The improvement in treatment delivered the required reduction in risk for concentrations of THM and cryptosporidium oocysts. Treatment achieved a 75 % reduction in colour. Not all of this reduction translated into a THM reduction since the reduced input of organics into the distribution network resulted in a substantial rise in chlorine concentrations. Even with the increased persistence of chlorine in the distribution network a reduction in THM concentrations of 40 to 55 % has been achieved, demonstrating that removal of precursor material is a fundamental requirement to achieve THM compliance whilst retaining a chlorine disinfection system.