Of all the earth's resources water is most common and exists in massive quantities. covering more than seventy per cent of the global surface. Present everywhere in nature, it is available in liquid, solid as well as in vapour forms, and fills oceans, rivers and lakes, besides providing the underground reservoirs and enriching the air. Water, indeed, is the basic requirement of all living organisms. However, in spite of the abundance of water, there is going to be famine of potable water and our dependence on its supplies could bring about human and biological activity to a standstill. We need to understand its resources, distribution, availability and use in a rational and systematic manner. This book endeavors to cover several facets of water, especially its origin, age, properties and economics. Basic concepts have been adequately supplemented by appropriate illustrations and diagrams. The book will be useful for graduate, postgraduate and research students to acquire in-depth knowledge on the subject. It would serve as a valuable guide for further expansion of hidden scientific knowledge to bring about the sustainable development of water resources for the survival of future generations.