The Water Cooler

The intertwined tale of energy and water

A 60-Watt incandescent bulb
can consume up to 6,000 gallons
of water a year

by Rachelle Hill and Dr. Tamim Younos

Jaques Cousteau once said "sometimes we forget that the water cycle and the life cycle are the same." What Cousteau meant was that not only the human survival but also all life on earth totally depends upon water. But our modern world is also driven by energy use, without which human life on earth could be very primitive. We need energy for producing food and clean water, providing electricity in our homes, businesses and industries, and we need energy for transportation. We know that without energy modern human civilization cannot survive, but do we know that energy production also depends on water?

The conventional production of energy and power requires a huge amount of water. Without water, our energy and power generation systems will come to an abrupt stop. In the United States, for example, thermoelectric power plants consume 136 billion gallons/day of fresh water (Hutson et al. 2004; US DOE 2006), a number that translates to an average of 25 gallons of water to produce one kilowatt-hour (kWh) of electricity. Energy and power plants require water to scrub pollutants (generated from burning coal, for example), to cool and clean machinery (USDOE 2006) as well as to produce the steam necessary to turn huge turbines and generators. Production of other energy sources, such as oil and natural gas, often relies on re-injection of water into wells. Furthermore, some alternative energy sources, such as ethanol and hydrogen, require large volumes of water. As electricity demand rises, perhaps as much as 50% in the next twenty-five years (EIA 2006a; US DOE 2006) energy production will demand more water (Hightower et al. 2007).

How much water is used by various energy production and power generation technologies and what is the water use efficiency of these technologies? The basic information is generally available from scientific literature and governmental documents. However, these documents do not express water use for various technologies in a consistent unit. For comparison purposes, we show water usage in a standardized unit, i.e. gallons of water [use] per British Thermal Unit (BTU) which indicates pure energy as heat. BTU is unit that is applicable to all energy production and power generation methods. Basic conversion factors for Kilowatt-hours (KwH) are available from the American Physical Society literature, while heat rates and yearly production for specific fuel sources and power generation methods can be obtained from Energy Information Administration reports. Calculation results that compare water use efficiency (gallons/BTU) for various energy production and power generation technologies are shown in Table 1 and Table 2, respectively.

Table 1 - Water use efficiency of various energy production technologies

*Heat Rate Conversions from EIA, 2007d

Table 2 - Water use efficiency of various power generation technologies

*Heat Rate Conversions from EIA, 2007d

Results show that in terms of energy production, biodiesel (soy-based) is the least efficient energy source followed by corn-based ethanol. Natural gas as an energy source is the most water efficient. In terms of power generation, nuclear energy is the least water efficient while hydroelectric power is the most water use efficient system.

The amount of water use (gallons per BTU) shown above appear to be insignificant, but consider the example of common household incandescent light bulb to understand ramifications. If we assume that a household will burn a single 60-Watt light bulb for 12 hours, it will yield 720-Watt hours for that light bulb or 0.72 Kwh. At present, fossil fueled thermoelectric plants provide about 53% of all power generated in the United States. The measure of efficiency (heat rate) for these plants will provide the necessary conversion of KwH to BTUs. The value for this heat rate is 10,022 BTUs per KwH (EIA 2007d). This means that for a fossil fueled thermoelectric plant as a source of energy a single light bulb will consume about 7,200 BTUs.

In terms of water use efficiency, it can be estimated that fossil fuel thermoelectric plants use between 1,100 to 2,200 gallons of water per million BTU to generate power (Table 2). This equates to approximately 8 to 16 gallons of water used to burn one 60-Watt light bulb for 12 hours per day. Over the duration of one year this one incandescent light bulb would consume about 3,000 to 6,300 gallons of water. It is estimated that there are about 111 million occupied housing units in the U.S. (United States Census Bureau 2005). If each housing unit was to burn one light bulb for 12 hours each day, over the course of a year, it would add up to 336 to 656 billion gallons of water use.

Afterthought

Our goal in conducting this study was to show that most conventional energy extraction and power generation technologies are water dependent, but some technologies need much more water than others. In the near future, increased energy development will compete for available water resources with other water demands such as irrigation, domestic water supplies and ecosystem services. Future production and cost of energy and power generation technologies will be impacted by the water availability. There is an urgent need to consider water availability (and protection) into energy and power generation policies. Some of the new energy initiatives such as biodiesel and ethanol production are in conflict with protecting water resources. The discussion in this article is limited to dependency of energy production on water. The article does not consider environmental impacts associated with various energy production and power generation technologies.

References

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