Ion exchange is the most appropriate technology to remove boron selectively from desalinated seawater. Reverse osmosis, necessary to reduce the salinity of seawater down to drinking water levels, can be combined with selective ion exchange. This combination reduces the overall capital cost and operating cost compared to an "all RO" solution. This paper presents the principles for an optimised combination and the detailed economics of this solution. The first plant in the world using the combined technologies was commissioned in May 2006.