Abstract: A balanced pressure tubular molecular filtration (Reverse Osmosis or Ultra Filtration) system in which semipermeable membranes are cast on or inserted into internal passages of a semiporous tubular substrate, and may also be cast on or affixed to the external surface of said semiporous tubular substrate, said tubular substrate also having one or more low pressure passages for collecting permeate water passing through said semiporous membranes, said tubular substrate being installed in a pressure vessel and operated in such a way that its external surface and all of its internal membrane coated passages are exposed to operating pressure, so that mechanical forces are in balance, thereby overcoming hoop stress and burst strength problems common to internal pressure tubular molecular filtration designs.