The water-energy nexus is the subject of huge debate and research: How can the United States meet future energy demands while conserving precious water resources? The focus has mostly been on how various energy sources impact both water quantity and quality, with little attention paid to what this means for fish and other freshwater biodiversity.

A new report from Nature Conservancy scientists fills that void by looking at how much water various energy technologies will consume in coming decades and how this could affect freshwater species. The findings show how U.S. energy choices could also save water resources—which will come under increasing pressure from population growth and climate change.

Energy Water-Use Impacts on Imperiled Fish

The study, just released in the peer-reviewed journal PLoS ONE, assesses the water needs of 12 energy production techniques—from hydropower, solar and wind to liquid fuels (petroleum, biofuel], coal, nuclear and more—and projects the regional impacts that various energy development scenarios could have on fish.

“Looking at energy development at the regional level, rather than national, is key for understanding what the real impacts could be,” explains Rob McDonald, a Conservancy scientist and lead author on the report.

The study finds that, by 2035, energy-sector water use could go up in some regions (the Southwest and Southeast U.S.) but down in others (Midwest and Northeast). Unfortunately for fish, the regions with expected energy-water increases are also where the highest numbers of imperiled fish are already found.

Fish with small geographic ranges—like most desert minnows and trout in the Lower Colorado River—have the highest risk for problems associated with increased energy-sector water consumption, says Julian Olden, a coauthor on the report and professor of aquatic and fishery sciences at the University of Washington, Seattle.

He points to the Rio Grande silvery minnow: Already one of the most endangered fish in North America, this species’ native range has been reduced to a single stretch of river between New Mexico’s Cochiti Dam and Elephant Butte Reservoir—just 7% of its historical range, says Olden.

“Many of these fish are already in a massive battle against extinction,” he says, citing the challenges of limited geographic range, small population sizes and low tolerance to human impacts such as dams, land-use change and pollution.

Saving Energy Saves Water & Fish

But the U.S. has, as they say, bigger fish to fry than—well, fish—when it comes to energy decisions. The report aims to emphasize the choices we do have, explains McDonald.

“We want to call attention to the critical point U.S. energy policy is at and remind people that saving energy means saving water,” says McDonald.

The energy sector is responsible for more than half of all water withdrawals in the United States—more than the agriculture industry. Water is used to power electric plants, mine coal, process petroleum, irrigate biofuel crops, and more. While only a fraction of the water withdrawn is consumed* (most is returned to the system, in some altered state), energy demand is expected to increase in coming decades. What solutions are there for energy-related water savings?

While the report refrains from compiling a list of “bad” or “good” energy choices, there are some interesting findings that energy policy experts should pay attention to. For instance:

• Hydropower is the largest user of water, and this coupled with structural impediments (dams, impoundments, etc.) have a high impact on fish;
• Coal and nuclear energy are the next highest withdrawers of water;
• Changes in how thermoelectric plants operate (from once-through cooling to recirculating cooling) could result in huge water savings;
• Biofuel production also requires a large amount of water to irrigate crops (mostly corn and soy in the U.S.);
• Natural gas typically has low water withdrawal intensity, but new technologies such as extraction from shale require more water;
• Wind and solar have some of the lowest water needs.

Again, regional differences come into play: For instance, evaporation off reservoirs—which accounts for nearly all the water consumed in energy production by hydropower—is higher in arid climates than humid ones. Of course, drier regions are exactly where water storage is more important.

And topography matters: Hydropower in South Texas has the largest estimated water consumption because of the region’s dry climate and relatively flat terrain, which results in wide, shallow reservoirs with high evaporation.

Energy policy invariably involves complex tradeoffs, notes McDonald. He highlights this example: Switching thermoelectric plants from once-through cooling to recirculating cooling (which could come as part of new EPA regulations) will reduce water withdrawals and thus benefit river health. But it will not significantly reduce water consumption—and the latter has a bigger influence on fish survival rates.

No one has a crystal ball to predict the future—from how climate change will impact water supplies to how U.S. energy policy will evolve at federal or state levels—but one thing is certain: The future of energy in the U.S. is at a turning point. It is a time of rapid exploration into new energy technologies to meet a growing demand, and the decisions made now will affect water availability for the future.