Pre-treatment of water is essential in order to minimise the impact to the RO membranes. Techniques such as deionisation, water softening, descaling, pre filtration, degasification (can be located between the stages of a double pass RO system), nanofiltation, electro-deioI1isation, ozonation, UV treatment and micro-filtration should all be considered during the design phase to assure the quality of the water produced.