In large public water parks, the water consumption is a significant part of the everyday operating costs. One major part of this consumption is caused by the sand- or multilayer screens for the pool water treatment, especially when these are back flushed for the purpose of cleaning them. With the release of the DIN 19645:2006 and the use of a two stage membrane filtration process it is now allowed to recycle this back flush water and reuse 80% of it within the pool water system. By this it is possible to save on freshwater costs, sewage water costs and energy costs and cut down on the everyday operating costs.