Limits on freshwater availability:
Although 70% of the earth's surface is covered with water, most of that is saltwater. By volume, only 3% of all water on earth is fresh-water, and most of it is largely unavailable (Duddin and Hendrie, 1998) since it exists in the form of ice located in remote areas far away from most human habitation; only about 1% of all available water is easily accessible, surface freshwater. This is mainly the water found in lakes and rivers. Overall, only 0.007% of the world's total supply of water is considered easily accessible for human use (Lefort, 1996).
The U.S. population has been steadily increasing from 1990s to 2000s. Among the 50 states, Nevada and Arizona experienced the highest population increase rates, which are 66% and 40%, respectively. The intermountain states have an average increase of 30%. Apparently, the southern states have faster population increase because of the available undeveloped territory and immigration. The future population in the U.S. is also estimated to increase by as much as 82% (from 296 to 438 million) in the U.S (Passel and Cohn, 2008). The following table shows the projected population of the United States from 2000 to 2010 (In thousands):
| Year | US Population (In thousands) |
| 2000 | 282,125 |
| 2010 (est) | 308,936 |
| 2020 (est) | 335,805 |
| 2030 (est) | 363,584 |
| 2040 (est) | 391,946 |
| 2050 (est) | 419,854 |
Sorce: U.S. Census Bureau, 2004, "U.S. Interim Projections by Age, Sex, Race, and Hispanic Origin," <http://www.census.gov/ipc/www/usinterimproj/>
In the U.S., local, regional, and statewide freshwater shortages occur frequently,
with parts of 36 states experiencing freshwater shortages under normal conditions and 46
states under drought conditions (USGAO, 2003). Washington, Idaho, Texas, Alabama,
Georgia, Louisiana, Florida and especially southwestern regions of the U.S. are
susceptible to water supply constraints (Roy et al., 2003). The following figure shows the total water withdrawals by catagories in USA (in 2000).
Figure: Total Water Withdrawal by Catagory in USA (2000). (Source:
United States Geological Survey (USGS). Estimated Use of Water in the United States in 2000; USGS Circular 1268; March 2004. http://pubs.usgs.gov/circ/2004/circ1268/pdf/circular1268.pdf)
It is evident that water and energy issues are intricately related and cannot be addressed in isolation. With the increasing population and energy demand, the scarcity of freshwater will become a nationwide phenomenon.
