The overall conclusion is that although permeable concrete block pavements cannot drain a traffic area entirely, they can still have a considerable impact on the run-off process of the entire catchment area. Due to the fact that part of the rainfall is retained, this part is not added to the run-off total and it can dampen the run-off peaks because of its delaying effect. In view of an overloaded sewer system this is of considerable ecological importance since the overload can be reduced by permeable concrete block pavements thus also avoiding discharge into the receiving water with the accompanying pollution. The respective relation between surface run-off and actual infiltration means for the hydraulic sizing of a drainage system that a more precise design method can be applied.