Abstract: A liquid flow device includes filter tubes which act as reverse osmosis tubes, ultrafiltration tubes or microfiltration tubes. The device also includes a stack of discs having apertures defining a plurality of elongated passages; an end disc provided at each end of the stack of discs; and a membrane tube provided in each elongated passage and projecting at opposite open ends through and beyond the end discs. A liquid inlet feeds liquid into the interior of at least one membrane tube; and a liquid outlet withdraws liquid from inside the membrane tubes. Tubular interconnector members are provided at both open ends of at least two of the membrane tubes for interconnecting the open ends of the various membrane tubes at both ends.