THE PROBLEM OF FRESH WATER
Water is unique among human necessities in the enormous quantities used - mainly for agriculture. For example, California uses 35 million acre-feet per year, i.e. a bit more than an acre-foot for each of its 30 million inhabitants. Because of this quantity, the main cost of water is transporting it. Oil can be imported profitably to the U.S. from the Persian Gulf, but moving water is costly. (Note that an acre-foot (an acre covered a foot deep) is about 7,755 barrels or 1233 cubic meters, and the price for an acre-foot of agricultural water is only a few times the price of a barrel of oil).
2004 update: The current estimate for California is 43 million acre-feet per year including agriculture. Sizes by John Lord published in 1995 says
At current American rates of consumption, on average one acre-foot of water is enough to meet the industrial and municipal needs of four people for a year.
There have been proposals to desalinate sea water in places that run short. According to the Britannica article on desalination, about 8 million cubic meters of desalinated water is produced per day, mostly in the Arabian Peninsula. This amounts to 2.4 million acre-feet per year. We could use desalinated water in California if we had to, but we probably wouldn't use it to grow alfalfa. See desalination further down on this page.
عمل الطالب:- علي مطلق الوسمي المطيري
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السبت 15 ديسمبر 2012, 05:15 من طرف adelahmed
