It is planned that the assessment of precipitation runoff for discharge into surface waters in Germany will be carried out in the future using the parameter PM63 [AFS63] (fine solids with a grain size of > 0.45 μm and < 63 μm). While centralized treatment structures have already proved their effectiveness and can be dimensioned according to existing codes and regulations, there is no evaluation procedure for decentralized treatment plants.

In principle, a reproducible laboratory test method that is based on the existing test method of the German Institute for Building Technology [Deutsches Institut für Bautechnik (DIBt)] is suitable for discharging rainfall runoff from traffic areas into groundwater. It must be adapted to the hydraulic feed and the choice of suitable test materials, for example, to be able to classify the efficiencies, as published in the new guideline DWA 102 in relation to PM63 [AFS63] for decentralized rainfall water treatment plants, and to be able to implement the provisions of the new Annex of the Wastewater Ordinance pertaining to rainwater.