If droughts, heat waves, and power plant troubles aren’t strong enough signals that power plant water use is something worth paying attention to, maybe this week’s approval of an energy-water resolution by NARUC, the national association of utility regulators, can help. Understanding the importance of actions like NARUC’s (and Mother Nature’s) depends on understanding how much water U.S. power plants use, and why. It’s a good time to take stock of what we know about that issue.
Mixing electricity and water
In thinking about how power plants use water, three issues to consider are why, what, and how much.
Why – While hydropower might be the first thing that comes to mind in thinking about the power sector’s using water, it turns out that lots of other kinds of power plants are also water-dependent, mostly for cooling the steam as a key part of making electricity from burning stuff (think coal, for example) for boiling water.
What – Water use is an ambiguous term, so maybe think of it this way: use comes in two basic forms. Withdrawal is the amount a power plant takes from a river, lake, ocean, aquifer, or other water source. Consumption refers to the water that doesn’t make it back, that gets evaporated in the cooling process.
How much – So what does that water use add up to? The Freshwater Use by U.S. Power Plants report from the UCS-led Energy and Water in a Warming World initiative (EW3) introduced an approach for calculating power plant water use. That approach, also captured in this EW3 team manuscript in a recent focus issue of Environmental Research Letters, found that, in the year analyzed (2008), U.S. power plants:
- Withdrew some 50 trillion gallons (or between 26 trillion and 74 trillion gallons) of water
- Consumed 1.6 trillion gallons (or between 1 trillion and 2.3 trillion gallons) of that water
- Used freshwater (non-ocean) sources for 86 percent of those water withdrawals and 96 percent of the water they consumed.
If picturing 50 trillion gallons isn’t easy for you (it isn’t for me), here’s how we put it in Freshwater Use:
Take the average amount of water flowing over Niagara Falls in a minute. Now triple it. That’s almost how much water power plants in the United States take in for cooling each minute, on average.
On a daily basis, the freshwater portion alone is on the order of 100 billion gallons withdrawn and several billion gallons consumed.
A single large power plant using once-through cooling can easily draw in a billion gallons in a day. Picture an Olympic-sized swimming pool, then imagine a plant emptying that in less than a minute, and then coming back for more the next minute, and more, and more.
The bigger picture
Another way to think about it is to put power plant water use in the context of water we use for everything else that needs watering: farm crops, factories, us (showers, sinks, washing machines, and more), etc.
When it comes to withdrawals, it turns out that power plants are number one, even edging out the agricultural sector. The U.S. Geological Survey (USGS) found that the power sector was responsible for more than 40 percent of freshwater withdrawals in 2005.
On the consumption side, agriculture was the big one; much of the water that gets put on fields doesn’t make it back out. But power plants were a fifth of the remainder, or 3.3 percent overall, according to the USGS, in 1995.
The even bigger picture
The wide ranges for power plant water use in the withdrawal and consumption data above, and the age of the pie chart data (1995? We’re depending on data that are old enough to drive?), are causes for concern. But there’s progress being made on those fronts, which is a subject for a future post.
And there are lots of other reasons to be encouraged about power plant water habits in general. Water-smart decisions are coming from the power sector, such as retirements of old, water-heavy coal plants, and lots of positive movement on water-frugal wind and solar technologies.
And now NARUC has weighed in, which is important given public utility commissioners’ important role in fomenting water-smart power sector decisions, and the role of knowledge in decision making.
If information is the currency of democracy, as has been said (whether by Thomas Jefferson or someone else), understanding power plant water data is a chance to get a little richer, and a little more democratic. More power to us.
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