Abstract: A self-contained, transportable reverse osmosis water purification unit has a limited throughput of no more than about 20 gpm of permeate in a single pass operation with reverse osmosis ("RO") modules which can be cleaned in place. When raw water is particularly fouled, the unit is operated in a double pass operation in which the permeate from the first pass is used as feed for a second RO module. The unit, referred to as a "purification container" "PC" or an ADROWPU because the PC is air-deliverable, comprises an enclosed weather-tight housing having a base on which the major components are removably mounted. For transportability, the PC has the overall dimensions of an ISO container, and is fitted with means to load and unload it on standard carriers. A high pressure pump is required to feed water freed from suspended solids to the RO modules.