The grey water from the shower, sink and bath are drained to the storage tank. The light polluted grey water is first biologically cleaned in the storage tank. The water is actively cleaned by reducing organic impurities with the use of a computer controlled ventilation. The biologically cleaned water is then forced through the membrame filter after which it is stored in the clean water tank. From the clean water tank the water is pumped to the secundairy water network by a pump, according to demand. This water network is connected to the washing machine, garden taps, urinals and toilets. If the clean water tank is running low on water, it will be filled from the rainwater tank. If this rainwater tank is also running low, or is not present, than the system automatically switches to drinking water;