Water Resources: Increasing Demand and Scarce Supplies
Kenneth D. Frederick
Water is one of the most readily renewable of the earth's natural resources. Globally, the total quantity of water is essentially constant and is unaffected by human activities; water can be used and reused virtually indefinitely. Evaporation removes the impurities in water picked up from natural and human sources. On the other hand, water is one of the least predictable resources. The hydrologic cycle continuously circulates water from lakes, streams, and oceans through evaporation and from plants through transpiration to the atmosphere, from where it eventually precipitates back to the earth. Water is commonly characterized as a fugitive resource because it naturally flows from one location and one state (liquid, gas, or solid) to another. These characteristics present challenges in managing, controlling, and allocating the resource.
Water also is a vital and versatile resource. It is essential to all life, and a secure supply is required for successful economic activity. Drinking remains the most critical use for human life, but much larger quantities are used for economic and recreational