A system to be incorporated in new or in existing buildings where the waste lines of lavatory sinks, showers and clothes washing machines are connected to a storage reservoir for accumulation of water therein. This accumulated water is filtered and treated and thereafter used for the operation of water closets of toilets, the storage reservoir providing for the gravitational separation of solids from the water which are periodically flushed from the reservoir into the sewer. The pumping action which delivers the accumulated water to the water closets of toilets may be hydraulically operated by a portion of the water drained to the storage reservoir.