Water desalination

A desalination plant (10) is disclosed which includes a pump for pumping water at a pressure of between 50 and 65 Bar to a generally cylindrical filter element (30) which includes a plurality of reverse osmosis membranes defining salt passages. Immediately upstream of the filter element (30) there is a disc (40) with a plurality of holes (44) in it. The disc (40) forms an obstruction which causes a pressure drop between the upstream side thereof and the downstream side. It also divides the water flow into a series of separate streams which impinge on the end of the filter element and flow into the salt passages. The water downstream of the obstruction is not only at a lower pressure than the water upstream of the obstruction but also is flowing turbulently. The disc (40) and filter element (30) are in a cylindrical casing (12). The brine which emerges from the filter element, and which is still at a substantial pressure, can be fed through a device such as a Pelton wheel to recover some of the residual energy therefrom.