The Zweckverband der Abwasserregion Olten (ZAO) is an association of 13 municipalities which treat their wastewater in the WWTP Winznau. The WWTP itself was and is already the subject of refurbisching measures, but other structures in the sewer network also showed a considerable need for refurbischment, including pumping stations and storm water tanks. Their automation was outdated, their work safety and work comfort no longer met today’s requirements. Control technology also allowed little leeway, because the drains were regulated purely mechanically, and the flow rates could neither be precisely set nor measured. Furthermore, the flushing dumps were not equipped with a monitoring system, which would have resulted in a very high drinking water consumption in the event of a defect.