customers with lower water demand may draw insignificant amounts without becoming a formal member. in cases of water shortage they have to renounce the supply for the benefit of the regular members. the need of service water varies very much – for example annually for a public pool 500 m³/year up to 15 mio. m³/year for a thermal power station. all together the withdrawal is on the average 60 mio. m³/year (with downward drift). the technically possible maximum of 400 mio. m³/year has never been used. the discharge of canal water via the stever into halterner stausee and talsperre hullern depends on the annual rainfall, for example the discharge in 1976 was 11.5 mio. m³ but in “wet years” nothing is discharged.