The need for a good quality water in the Canary Islands was, and continues to be, the driving force for the use of reverse osmosis to desalinate brackish water and seawater for irrigation and potable use. A number of case histories are presented which show the development of the use of reverse osmosis, from the small plants built 25 years ago in the early 1970s to current-day use. The case histories show not only the increase in use of reverse osmosis but also plot the development of the performance of the available membranes. The case studies show the importance of bringing previous experience to the design and direct technical support to the customer by the membrane supplier in order to ensure satisfactory long-term stable system performance.