Abstract: A reverse osmosis (RO) unit uses a membrane permitting operation at abnormally low water pressures, typically as low as 10 PSI. Because any requirement for a pump to boost inlet water pressure is obviated, the RO unit makes do with only one, small and compact, outlet pump. An optional single, or a dual-channel dual-pass, ultraviolet (UV) light source sterilizes filtered inlet, and/or the purified output, water flows. Purified water is stored at atmospheric pressure in a simple storage bag, and is dispensed on demand by force of the outlet pump. The entire RO unit--storage bag, pump, filters, UV sterilizer, membrane and all--is preferably entirely integrally packaged in a compact and aesthetically pleasing cylindrically-shaped housing. The RO unit so housed is suitably deployed on a household counter top while flow-connected to normal household plumbing--typically to the faucet and drain of a kitchen sink--and while electrically connected to normal household power.