Rainwater; information on infiltration without a permit

Urban drainage used to mean draining rainwater as quickly and completely as possible in order to reduce the risk of flooding in the town. Nowadays, the aim is to minimize the impact on the natural balance of the water cycle by using rainwater in a "near-natural" way. This brings not only water management but also financial benefits. Rapid drainage of water impairs groundwater recharge and shifts the risk of flooding onto downstream residents.

The principle of all construction activities should be to intervene as little as possible in the water balance, for example by using water-permeable surfaces or green roofs. However, if intervention cannot be avoided, it can at least be limited by near-natural, decentralized rainwater management. Low-pollution rainwater (e.g. from roofs and courtyards, private and municipal roads) should therefore be infiltrated on site, collected and used (e.g. for watering gardens or flushing toilets) or at least retained decentrally and discharged in doses into streams and rivers. No permit is usually required for the infiltration or discharge of rainwater if the relevant technical regulations are observed.

Subject to Section 8, a permit is not required for the discharge of collected precipitation water into the groundwater (Section 9 (1) No. 4 WHG) if the essential requirements are met:

• The precipitation water is infiltrated over a suitable topsoil layer.
• Underground infiltration systems such as infiltration trenches, seepage pipes or shafts are only permitted if surface infiltration is not possible and appropriate pre-treatment is carried out.
• A maximum of 1,000^m2 of paved area may be connected to an infiltration system.
• Infiltration takes place outside of water and medicinal spring protection areas and outside of contaminated sites and suspected contaminated sites.
• The rainwater to be infiltrated is not adversely modified or mixed with wastewater or substances hazardous to water.
• The rainwater to be infiltrated does not originate from areas where substances hazardous to water are regularly handled (except for small containers up to 20 liters).
• Rainwater from uncoated copper, zinc or lead surfaces over ^50m2 may only be infiltrated after pre-cleaning the water via a suitable topsoil layer or after pre-cleaning via a treatment system with type approval (see "Metal roofs" subpage).