The book is intended to provide a basic understanding of how to judge existing potential for rainwater harvesting under different conditions and uses in Tanzania. It describes the physical processes that determine the availability of a rainwater, and then discusses the concept of water balance. It describes and discusses the factors that determine the potential of rainwater harvesting as well as different techniques suitable for various uses. It emphasizes the importance of ensuring social and economic viability and equity. It discusses the planning approaches and stages. The final section of the book highlights the importance of information technologies in any form of planning so as to sensitize the planners that the adoption of modern information technology is crucial to effective planning.