This paper is one of a series published by Volunteers in Technical Assistance to provide an introduction to specific state-of-the-art technologies of interest to people in developing countries. The lack of good, dependable, environmentally protected stores of water is a serious problem I many underdeveloped regions of the world. Improving this situation will require a substantial infusion of effort and money. It is hoped that the suggestions made herein will be valuable in stimulating new ideas. selecting the most suitable technology from among the various alternatives available, and applying the correct criteria to locate and size storage facilities.