the water demand for shipping nevertheless is important in the west german canal system. to compensate the loss of water from evaporation, infiltration and locking in the sluices annually 500 mio. m³ of water have to be injected. to reduce especially in dry weather periods the demand of water that gets lost from the sluices it is locally pumped up again. the total water demand from the canal system of up to 800 mio. m³/year is mainly covered by supply from the lippe and ruhr.