The shortage of fresh water supplies is one of the main threats to sustainable development. Membrane technologies such as reverse osmosis (RO) have been used for over twenty years to treat sea water (SWRO) and waste waters. The applications have been limited due to the sensitivity of RO membranes to fouling and the ability of conventional pretreatment technologies. Pretreatment represents a real problem in the SWRO process. It represents 22.97% of the total product water costs at the Doha Reverse Osmosis Plant producing 4546 m(3)/d [1]. The development of backwashing continuous microfiltration (CMF) membranes enables RO to desalinate variable feed waters including turbid waste waters. Completed projects include the desalination and reuse of brackish secondary sewage and eutrophic surface water for industry and irrigation. These installations have resulted in a 40% reduction in the sizing of the RO plant installed, a 60-90% reduction in chemical used and effluent costs for the conventional deionisers, as well as solving local environmental issues through the reduction in potable water use and waste discharge.