Measuring the Water Footprint of the Energy We Consume

As Japan’s nuclear power plant emergency has highlighted, water is needed in copious quantities to generate energy. To mark World Water Day, Sandra Postel (National Geographic) considers the huge water footprint of energy generation. According to USGS, thermal power plants (fuelled by coal, oil, natural gas or uranium) account for 49% of water withdrawn.

We don’t think much about water when we flick on a light, power up our computer or open the fridge for a drink. But water has been consumed for almost every activity that uses energy – which includes almost everything we do. The single biggest draw on US rivers and lakes is not toilets, golf courses or even irrigated farms: it’s thermal power plants that generate electricity to light our homes and cities, run appliances and factories and generally keep our plugged-in society humming.

Thermoelectric generation accounts for 49% of the water withdrawn from the nation’s water sources, according to the US Geological Survey. On average it takes about 23 gallons of water to produce 1 kilowatt-hour of electricity. That means a typical refrigerator can use 40 gallons of water a day – not at your home, but at the power plant that produces your electricity. Thermal power plants (fuelled by coal, oil, natural gas or uranium) boil water to produce steam, which then drives a turbine to generate electricity. These fossil fuel and nuclear plants produce about 90% of the electricity used in the US.

The vast majority of these plants are situated on a river, lake, estuary or bay because they require copious amounts of water for cooling. In contrast to irrigation, which ‘consumes’ a great deal of water due to evaporation losses and crops’ transpiration of water back to the atmosphere, most thermal power plants consume little of the water they withdraw. Most operating plants use the older ‘once-through’ systems that release cooling water back to its source. However, the heavy extractions and discharge ofwastewater warmed by as much as 20–30 degrees can degrade water quality and kill large numbers of fish and other aquatic organisms.

The Indian Point nuclear power plant, located along the Hudson River 24 miles north of New York City, kills nearly a billion aquatic organisms a year according to New York State officials. Among them are shortnose sturgeon, an ancient fish that has plied Earth’s rivers for millions of years but is now at high risk of extinction. Indian Point’s two operating reactors together withdraw an astonishing volume of Hudson River water – some 2.5 billion gallons a day. That’s nearly two-and-a-half times the daily water use for all of New York City.

Last year New York officials ruled that operation of the Indian Point reactors killed so many fish and degraded water quality to such a degree as to violate federal and state water standards. Entergy Corporation, the plant’s owner, now faces the prospect of having to invest $1.1 billion to upgrade the plant’s once-through cooling system to a closed-cycle (or re-circulating) system, which requires about a tenth as much water and kills far fewer fish. Entergy’s licenses to operate the two reactors expire in 2013 and 2015, respectively, and a state-issued water quality certificate is needed for a 20-year renewal of the licenses.

Along with fish kills and water quality, there is also growing concern about the reliability of river flows needed to cool thermal power plants. During the severe drought in the southeast US in 2007, the Browns Ferry nuclear plant along the Tennessee River in Alabama reduced electricity production due to high water temperatures and low river flows. The previous year, Alabama Power Company went to court over worries that a federal plan to release water from Georgia reservoirs to protect endangered mussels downstream in Florida would leave too little flow to cool its Farley Nuclear Plant.

Electricity, of course, is only a portion of our energy use. Fuel for heating and transportation also requires water. Hidden within each gallon of petrol we pump into our cars is about 13 gallons of water. All together, energyaccounts for about 35% of the average American’s water footprint.

It’s critical that we begin to grapple with the reality that energy and water are tightly entwined. All too often, policies and choices aimed at solving one problem make the other one worse.

Likewise, it makes no sense to site nuclear power plants where water supplies are scarce or unreliable. On the heels of the nuclear crisis in Japan, New York’s Governor Andrew Cuomo said on March 16 that Indian Point should be closed, because one of its reactors sits on a fault line and poses unacceptable safety risks.

Sorting out this nexus of energy/water challenges will not be easy, but the good news is that saving energy saves water and there are still many opportunities to reap gains from this win-win. Improving the efficiency of our lighting, heating, appliances, cars and transportation systems can save billions of gallons of water and also protect fish and other aquatic life – which is something we should be thinking about not just on World Water Day but every day.

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The Copenhagen accord disappointed most of us for various reasons. What rankled me above all was the absence of a pivotal climate change ingredient – water. Copenhagen delegates deliberated on reducing the carbon footprint but neglected the water footprint embedded in any unit of energy. We failed to appreciate that water, energy and climate change are inextricably linked.

Water and energy are cardinal to every aspect of human life. Both are interdependent – water is used in the generation of energy while energy is needed to supply water. Their use depends upon and impacts our eco-system, which is already under stress and running short of both these resources. Further, limitations on water usage are restricting our plans of generating more energy, while energy shortages are curbing our supply of clean water. And this intense competition between the two resources is amplifying with increasing global demand for water and energy, coupled together with climate change effects.

Water Used in Energy

The thermoelectric power sector is the second largest consumer of water resources in the United States, irrigation being the largest. More than 40% of freshwater is used for thermoelectric power generation; albeit a large part of this is recovered with degraded quality and higher temperatures. Water is used extensively, from cradle to grave, in all stages of energy production: resource extraction, refining, processing, electricity generation, storage and transport. Of course, with advancements in technology the fraction of water consumed by power plants is decreasing. However as demand for water increases, it is expected that water will limit our solutions for producing more energy.

Before looking at our water footprint for energy, it is noteworthy to understand two different estimates of water usage available widely – “water consumption” and “water withdrawal.” The former pertains to water that is used-up in energy production (either due to evaporation or contamination etc.) and unfit for returning to the original source. Water withdrawal, on the other hand, refers to removal of water from its original source; whether this water is later consumed or recovered is not accounted for.

Based on this definition, let us look some major water-consuming power plant types and their “water withdrawal” and “water consumption” rates, per MWh of electricity. Although analyzing water consumption would perhaps make more sense, a large part of the existing literature discusses “water withdrawal” rates. I have compiled these numbers together from various sources: EPRI, “Water & Sustainability;” NEI, “Water Use, Electric Power, and Nuclear Energy;” World Economic Forum & Cera, “Thirsty Energy;” Scientific American, “Energy versus Water.”