Ultrafiltration has proven to be suitable for the reuse of backwash water from rapid sand filtration. The permeate can be used directly as drinking water; for safety reasons UV disinfection was installed. In this way the water loss of drinking water production from groundwater is reduced to less than 0.5%. It is cost effective due to the groundwater tax of $0.15 in the Netherlands. Results are presented for a 100 m(3)/h plant.