Abstract: In a offshore oil and gas platform located over seawater in an open sea environment, the platform having drilling equipment, crew quarters, and a potable water holding tank for holding potable water, a portable desalination apparatus for producing potable water from seawater. The apparatus is comprised of a support skid to which is mounted a plurality of removable lifting lugs. A pump with associated piping and valves are fixed to the skid for collecting seawater from the open sea environment. Additional piping and valves are provided for moving seawater from the pump to a seawater filter. Additional piping and valves are used for moving the filtered seawater to a plurality of first pressure vessels each having reverse osmosis elements to produce a first quantity of brine water and a first quantity of desalinated water from the filtered seawater.