Abstract: A method for purifying water comprising at least one member selected from the group consisting of organic and inorganic particles, involving supplying water to a collection surface forming above an outlet of a filtration apparatus including filler material in an amount sufficient to cause the formation of bubbles in a trickle stream flowing through the filtration apparatus and forming foam on the collection surface by utilizing the bubbles, binding a major part of the at least one member selected from the group consisting of organic and inorganic particles in the foam, and skimming the foam off the collection surface into an area above the collection surface under pressure compensation.