The invention relates to a method and a device for purifying water used for forming a water curtain of a wet spray wall in paint spray and/or glue processing booths, wet dust removal plants and the like. The water to be purified is caught in a receptacle (1) and the water is sucked out under the surface of the water present in said receptacle (1), mixed with air and introduced into a basin (14) at the bottom side of said basin (14). The water mixed with air is introduced into a basin (14) which widens in upward direction, and contaminations floating on the surface of the water present in said basin (14) are pushed towards an outlet disposed near one side of said basin (14) by means of a pusher, whilst the water flows out on the opposite side of the basin via an overflow. A few perforated plates disposed one above the other are provided in the basin (14) whose sectional area gradually increases in upward direction.