Precipitation water; information on permit-free infiltration

Precipitation water from paved areas is to be returned to the natural water cycle as far as possible (= near-natural rainwater management).

Description

In the past, urban drainage meant draining precipitation water as quickly and completely as possible in order to reduce the risk of flooding in the town. Nowadays, the aim is to have as little impact as possible on the natural balance of the water cycle through the "natural" handling of rainwater. This brings not only water management but also financial benefits. Rapid drainage of water impairs groundwater recharge and passes on the risk of flooding to downstream residents.

The basic 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 the impact cannot be avoided, it can at least be limited through near-natural, decentralised rainwater management. Therefore, slightly polluted rainwater (e.g. from roofs and courtyards, private and communal roads) should be infiltrated on site, collected and used (e.g. for watering gardens or flushing toilets) or at least retained in a decentralised manner and discharged in doses into streams and rivers. In most cases, no permit is required for the infiltration or discharge of precipitation water if the relevant technical rules are observed.

Prerequisites

For the discharge of collected precipitation water into groundwater (§ 9 para. 1 no.. 4 WHG), a permit is not required, subject to § 8, 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 permissible if surface infiltration is not possible and appropriate pre-treatment is carried out.
  • A maximum of 1,000m2 of paved area may be connected to an infiltration system.
  • Infiltration takes place outside of water and medicinal source protection areas and outside of contaminated and suspected contaminated sites.
  • The precipitation water to be infiltrated is not adversely altered or mixed with waste water 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 of up to 20 litres).
  • Rainwater from uncoated copper, zinc or lead surfaces over 50m2 may only be infiltrated after the water has been pre-cleaned via a suitable topsoil layer or after pre-cleaning via a treatment plant with design approval (cf. subpage "Metal roofs").

Links to more information

Status: 04.11.2021

Responsible for editing: Bayerisches Staatsministerium für Umwelt und Verbraucherschutz

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