On natural, unsealed areas evaporation is the main part of the water balance among surface runoff and percolation. In Germany, an average of 60 % of precipitation evaporates on unsealed areas. If the intend is a natural hydrological balance, great importance is attached to evaporation. Besides, measures for rainwater harvesting, that have a positive impact on evaporation can contribute positively to climate (heat island effect- see green roofs). In Central Europe, a complete evaporation of the total precipitation is however not possible to be achieved and would also not meet natural conditions. Therefore, those measures need either a derivation component or a combination with storage (e.g. see Infiltration and retention structures).