Abstract: A filter assembly especially suitable for filtering swimming pool water includes an upright tank, and a flexible, cylindrical porous filter bag supported on star shaped core elements which are vertically spaced along a perforated outlet tube fixed centrally within the tank. Water normally flows through a filter media such as diatomaceous earth caked on the outside of the bag into the central tube and out of the tank back to the pool. When the bag becomes clogged by dirt trapped on the outer face of the filter cake, water flow is reversed for a short period of time to expand the bag suddenly and thereby release the dirt. The bag and filter media are regenerated periodically in this fashion to prolong the effective performance life of the filter.