Treat process wastewater, discharge into the mains drainage system? Comply with water legislation!

Where to put the process wastewater? Anyone wishing to treat process wastewater and discharge it into the public mains drainage system must comply with the requirements of their regional water management authority. After all, economical but at the same time sustainable use of the resource water is not possible without professional water recycling. Which legal regulations shape the design of modern wastewater treatment in Germany?