Repeated water quality analysis revealed that the amount of iron _and manganese in the raw water was higher than initially expected. It became necessary to add a new rapid sand filter. Introduced ProMix system, monitored turbidity _and flow rate, adopted flocculant PAC _and linearize control for proper hypoinjection. The amount of drug injection has been reduced, _and management has become easier. Cost reduction is also realized by reducing the amount of chemicals. The turbidity of the treated water is stable at <0.1.