The vital economic activities of the islands of the County of Split and Dalmatia are in the area of agriculture and tourism. Providing sufficient water supplies stands as an essential condition for their economic development, particularly with respect to the development of the two vital economic activities of agriculture and tourism. The use of renewable energy sources at Croatian islands is looked on as a necessity and represents a fundamental condition for their sustainable development. The paper presents the main features of the existing, built and planned, water supply systems on the islands of the County. Furthermore, the paper is an analysis of the place and role of the wind-driven seawater desalination plant in ensuring the water quantities indispensable for the proposed development of agriculture, as well as the analysis of the main features of the investments related to this development.