To customers the most obvious manifestations of the removal of organic material is the change in the colour of the water. Monitoring of colour at a fixed point in distribution systems showed that for Watchgate true colours fell by 80 % from 10 Hazen to about 2 Hazen (Figure ). As the data shows, this reduction has been maintained through the winter months when there had been concern that performance might deteriorate due to the higher loading and reduced removal efficiency at the lower temperatures. Averaging over the supply area gave an average reduction in colour of about 75 % in both the Oswestry and Watchgate systems (see Table ).