The Water Footprint of Energy

In water to make energy, water use

 

Electricity and Virtual Water Use

In the US, almost 90 percent of electricity is generated by thermoelectric power plants. These facilities use fossil fuels – primarily coal, oil and natural gas – or nuclear fuels to boil water for steam to turn turbines and generate electricity. Once the steam is used, it has to be cooled. Sometimes the water is reused or recycled back through the system, but often it is used only once – what’s known as “once-through” cooling systems – after which it is sent to a cooling pond or returned to the water body from which it was withdrawn, but at a higher temperature. About 43 percent of power plants in the United States use once-through cooling systems. The remaining 57 percent use less water-intensive “closed-cycle” systems – where cooling water is recirculated – or “dry-cooled” systems (where air is used for cooling instead of water).

Because of the large amount of water required by thermoelectric plants, total US withdrawals for thermoelectric power accounted for 41 percent of total water withdrawals in 2015 (the most recent year data is available). That added up to 133 billion gallons per day, most of which were from surface water sources and 72 percent of which were from freshwater sources like lakes and rivers.  Power plants that used
once-through cooling systems accounted for 96 percent of all withdrawals for thermoelectric power.

In addition to the large volumes of water required, once-through cooling systems can have devastating impacts on aquatic ecosystems. As water is drawn into the plant, fish, fish eggs and other aquatic life can be injured or killed in the process.

In addition, when the cooling water is put back into the water body from which it came, it is typically warmer than when it was withdrawn, potentially damaging aquatic life through “thermal pollution.” In fact, the main source of thermal pollution in rivers is cooling water from power plants. Many plants across the US have reported returning cooling water to source waters with temperatures above 90 degrees Fahrenheit, and some reported temperatures above 110 degrees Fahrenheit. This will become increasingly problematic as average air and water temperatures make record breaking increases every year due to climate change. More power to run air conditioners and HVAC systems will be required, which means more cooling water will be necessary. That cooling water will be harder to cool because of higher air temperatures and the water it will be returned to will be warmer, causing even more aquatic damage.

There are many renewable energy options available today, both large- and small-scale, that require significantly less water than thermoelectric power plants. Switching to clean, sustainable and water-friendly energy sources like wind and solar power is an important step toward reducing our energy-related water use.

Transportation Fuels and Water Use

Producing and refining transportation fuels like oil, natural gas and biofuels requires a lot of water. Researchers at the Lawrence Berkeley National Laboratory estimate that the United States withdraws one to two billion gallons of water to refine nearly 800 million gallons of petroleum products like gasoline every day. To complete all the steps required to produce a gallon of gasoline takes, on average, three to six gallons of water.

In the United States, there are regulations in place that require a percentage of transportation and heating fuel be replaced by biofuels – ethanol. While it can be produced from a variety of feed stocks, 95 percent of the ethanol produced in the US comes from corn, much of which is irrigated. As it turns out, what has been touted as an eco-friendly alternative fuel is not so water-friendly. This is because, at 10 to 324 gallons of water for every gallon of fuel produced, corn ethanol uses more water than gasoline. In addition, much of the corn used for ethanol is grown in Great Plains states that rely on the increasingly water-stressed Ogallala Aquifer as an irrigation supply.

Using Less Water by Using Less Energy

Driving less, carpooling and using public transportation are all good ways to reduce fossil fuel use and to save water. So, too, is using energy more efficiently at home by switching to energy- and water-efficient appliances and light bulbs and by turning off electronics when they’re not being used. Energy- and water-efficient appliances also play a critical role in conservation, because saving energy saves water, and vice versa. This reduces the strain on resources even further.

Small efforts to conserve energy and water really add up, and we each have the power to save.