uses of water

Water is one of the most vital natural resources for all life on Earth. The availability and quality of water always have played an important part in determining not only where people can live, but also their quality of life. Even though there always has been plenty of fresh water on Earth, water has not always been available when and where it is needed, nor is it always of suitable quality for all uses. Water must be considered as a finite resource that has limits and boundaries to its availability and suitability for use.

Figure 1. Offstream uses (depicted on the left) are those in which water is removed from its source, either by pumping or diversion. Instream uses (depicted on the right) are those in which water remains in place, and typically refers to stream (rather than groundwater). Where water supply is limited, conflicts may result between and among the various uses.

The balance between supply and demand for water is a delicate one. The availability of usable water has and will continue to dictate where and to what extent development will occur. Water must be in sufficient supply for an area to develop, and an area cannot continue to develop if water demand far outstrips available supply. Further, a water supply will be called upon to meet an array of offstream uses (in which the water is withdrawn from the source) in addition to instream uses (in which the water remains in place). Figure 1 represents the demands on water as a tug-of-war among the various offstream and instream uses.

Traditionally, water management in the United States focused on expanding or manipulating the country's supplies of fresh water to meet the needs of users. A number of large dams were built during the early twentieth century to increase the supply of fresh water for any given time and place. This era of building large dams has passed. In the twenty-first century, the finite water supply and establishedinfrastructure require that demand be managed more effectively within the available sustainable supply. Water-use information can be used to evaluate the impacts of population growth and the effectiveness of alternative water management policies, regulations, and conservation activities.