Abstract: This relates to methods and apparatus for filtering liquids such as oil contaminated water. The apparatus includes spaced apart supply and take-up reels capable of storing an elongated compressed ribbon of flexible open cell foam thereon. In operation the ribbon of filtering medium, in the uncompressed state, extends between the supply and take-up means across a support such as a grid or screen which permits free flow of water through the filter medium. The contaminated water is supplied to the upper side of an exposed section of the filter medium through a system which evenly distributes the contaminated water over the exposed section of the filter medium. The water passing through the filter medium may be collected in a suitable tank or basin. When the exposed section of filter medium becomes so loaded with contaminants (such as oil) that the flow through the filter decreases, the ribbon is advanced to expose a fresh section.