Following laboratory-scale research as part of the LIFE programme, a pilot plant with a capacity of 30 m(3)/d was built. This plant allowed the optimization of the parameters necessary for the engineering analysis, as well as the extrapolation of results and the development of a treatment plant with a capacity of 500m(3)/d. The latter includes all existing tertiary processes up to the latest generation and makes possible their sequential operation and the later integration of all the units, from the outflow onwards, into the Guia-Galdar wastewater treatment plant in Las Palmas de Gran Canaria. The initial phase consists of treatment using reversible electrodialysis (with a production of 100m(3)/d), ultrafiltration (430m(3)/d) and reverse osmosis (210m(3)/d). Six qualities of water are obtained which can be used for agricultural irrigation of specific crops. The feasibility of controlling both quantity and quality allows satisfying the demand. The project offers technological innovations and efficient solutions which are of special interest in areas where the water demand exceeds availability. It also has practical applications beyond those of a purely demonstration plant. Variations were introduced in order to adapt the system to the nature of the islands (type of outflows and end-use) which individualize the project.