This introductory book is for newcomers to the field of desalting. As a result of the development of arid regions, and also in the wake of intensive use of water in urban areas all over the world, fresh water is frequently not available in the quantities desired. In the last 20 years, great strides have been made in the development of the science and technology of water desalting. Statesmen, economists, scientists, and engineers must often make decisions relating to this field. Quite often such decisions involve the disposition of considerable amounts of energy and investment funds. It is hoped that this book will provide newcomers with sufficient background to appreciate the fundamentals involved, to understand the jargon of the "insiders," to guide them to the rich original multidisciplinary literature of this field, and to facilitate the first stages of further reading. Conversion of salt water into fresh water requires useful energy, i. e. , energy that could otherwise be used for mechanical or electrical work. Therefore, the problem of water desalting is intimately linked to power supply. A second, equally important factor in the economic balance is the availability and cost of equipment. The production of energy-efficient and reliable desalting plants requires considerable engi­ neering skill and usually a variety offairly sophisticated control devices.