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The Water Equivalent of Energy

June 1, 2010

Photograph of a small waterfall

(Image by Danny Steven)


If you came to this page via a
Google search, you unknowingly consumed a half milliliter of water, according to Robert Osborne, a Civil Engineer in South Carolina who publishes a blog at watercrunch.com. The reason this is true is that all power plants need large quantities of water to operate. Recall the large cooling towers that are associated with nuclear power plants. There are about 300 million searches performed daily, a number that corresponds to 150 000 liters of water, or a thousand bathtubs full. That's just one fact about the water equivalent of energy that's published in the current issue of the IEEE Spectrum magazine [1].

Of course, a Google search is one of the least energy-consuming things we do. The typical computer running that search requires several hundred watts of power. Even a cellphone needs about five watt-hours of charge, equivalent to about a half-liter of water. So, a conversion factor of about a liter per 10 watt-hours (100 liters per kilowatt-hours), when applied to the world's electrical energy demand of 17 billion megawatt-hours, gives an annual world water demand of 1.7 x 1012 liters. This is 4.65 x 109 liters liters per day. The US share of this daily use is about 500 billion liters, or twice the flow of the Nile River [2].

I mentioned Google search and the electrical requirement of the computer that runs it, but what about the the water needed to manufacture the computer? Intel has a yield of a few hundred Pentium CPU computer chips from each 300 mm silicon wafer. Such wafers require about 2,000 gallons of water to process [3], so each CPU chip has a water cost of about ten gallons. Much of that water must be ultrapure water, which is manufactured by an energy-intensive process.

Water demand in developing countries is rising at a rapid rate. Water reserves used exclusively for farming in the past now need to be shared with industry. Not only that, but the water from most industrial processes, unless purified, is returned to the environment in a toxic state that contaminates fresh water supplies. According to the World Bank, India's supplies of fresh water will be exhausted by 2050 if its present rate of development continues [4]. China, which has polluted about seventy percent of its water supplies, will run out of fresh water by 2030. [4] The 2030 Water Resources Group has published a 2009 study, "Charting our water future," that includes this sobering outlook of the state of the world's water supplies [3]:

Competing demands for scarce water resources may lead to an estimated 40 percent supply shortage by 2030.

References:

  1. The Coming Clash Between Water and Energy, IEEE Spectrum Online (June 2010), p. 12.
  2. Pure water, semiconductors and the recession, Global Water Intelligence, vol. 10, no. 10 (October, 2009).
  3. 2030 Water Resources Group, "Charting our water future" (2009).
  4. Cherian Thomas, Unni Krishnan and Sophie Leung, "China-India Water Shortage Means Coca-Cola Joins Intel in Fight," Bloomberg Online (May 26, 2010).

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