In this election year–notable for concerns both about the US energy future and extreme droughts in parts of the US and around the world–there is a remarkable disconnect between energy policy proposals and concerns about water quality and availability.

Yes, awareness is higher about water issues, stemming from the severe drought in Western states and the recent lead contamination crisis in Flint, Mich. But traditionally we view energy and water as separate concerns, when in fact they are inextricably linked.

Scientists recognize what is sometimes called the “energy-water nexus.” The nexus pulls resources in both directions. Vast water resources are used in some forms of energy extraction and production, particularly in mining or drilling for fossil fuels used for transportation and electricity generation and in mining and electricity generation using nuclear fuels.

Worldwide, annual water consumption for energy uses is projected to reach nearly 100 billion cubic meters in 2020.

Likewise, energy is used to make water resources available for human consumption through pumping, treating, desalinization and transportation.

On the energy side, the water connections are not always obvious. For fossil fuels, energy is used extensively in extracting and processing the fuels and also for cooling production equipment when the fuels are burned to produce electricity. Nuclear energy also uses huge quantities of water both in mining for uranium used to fuel nuclear plants as well as for cooling. A nuclear power plant, for example, uses up to 17 million gallons of water per day for cooling.

And even some forms of energy that are usually thought of as “renewable” consume large amounts of water. Biofuels–when produced from irrigated crops–require water both to grow the crops and again for cooling when they are burned.

Concentrating solar power, which like fossil fuels requires the energy it produces to be converted to electricity by a steam turbine, also uses large amounts of water for cooling. Even hydropower consumes some water – through evaporation while water sits in reservoirs at the heads of dams.

Both current policies and election driven proposals fail to recognize the important links between energy and water. President Obama has largely supported fracking and Hillary Clinton–until pressed by Bernie Sanders–generally took the same position. Donald Trump is advocating even greater use of fossil fuels, including coal.

The quantities of water consumed in these forms of energy production are stunning. Freshwater withdrawals for energy uses account for more than 40% of all freshwater withdrawals in the United States and about 11% of all US water consumption–or water that is not easily available for reuse. That comes to more than 12 billion gallons of freshwater per day consumed in the US for energy sector.

Where does the water come from? It’s surface water, groundwater, and water from rivers and lakes. So, the water used to produce energy is also drawn from the same sources used to supply drinking water, and to support agriculture and industry.

Some of the water is recycled in extraction and cooling processes, but large quantities of water are fully consumed and lost for other purposes, including drinking water. Large withdrawals of groundwater may also affect the quality of the water left in the ground by increasing concentrations of contaminants and heavy metals such as arsenic, lead, and radon, in the remaining water.

Particularly troubling from the water supply perspective is the growth in fracking for oil and natural gas extraction, which not only consumes enormous amounts of water, but also threatens contamination of drinking water supplies.

In fracking, millions of gallons of water are injected miles into the ground–along with chemicals and sand–to fracture shale rock in order to release oil and gas locked up in the shale. A single fracking well may use on average 1 million gallons of water.

Besides drawing on limited water supplies and forcing other uses to compete for available water, fracking also threatens the quality of water supplies at several stages of the fracking process. Much of the fracked water–contaminated with chemicals used in the fracking process–is subsequently injected into previously dug and abandoned mines. That contaminated water can leak into groundwater needed for drinking supplies. Groundwater may also be contaminated by spills or natural gas leaks at the surface of fracking wells.

Although the fracking industry contends that contamination of drinking water supplies is not a significant risk, the EPA and others have found that these risks are real and that such contamination has, in fact occurred.

This huge use of water for energy production is happening at the same time as devastating droughts in the United States and around the world.

In the United States, several western states are experiencing abnormally dry conditions and areas of California, Nevada, and New Mexico are facing at least moderate to extreme drought conditions. But these are also states where fracking is taking place. The same is true in parts of the North Dakota, Wyoming and Montana. Oklahoma, where much of the US fracking takes place, is also at risk of water scarcity.

Also concerning are other types of energy use that require large amounts of water where water availability may be limited or competes extensively with other uses like agriculture. For example, biofuel crops that require irrigation compete for water in the Great Plains where water scarcity is already an issue.

The scarcity issue is troubling in both directions. Water sources for drinking water and other uses are challenged by withdrawals for energy production. But energy supplies that are dependent on water availability are also threatened by water scarcity.

However, not all forms of energy require such massive water use. Indeed, wind energy and solar energy produced from photovoltaic panels use virtually no water at all. Likewise, these renewable energy sources are clean and do not threaten water contamination.

Arguments in favor of conversion to these forms of renewable energy are usually made in the context of limiting emissions of carbon dioxide and other greenhouse gases that contribute to climate change. Those efforts have been slowed by the continuing failure of the US Congress to address climate change and the Supreme Court-ordered halt to the implementation of the Obama Administration’s Clean Power Plan.

But it is also urgent that we look at the environmental consequences of energy choices beyond climate change. From a water use perspective, not all supposedly “clean” energy sources are the same. Looking at water usage, photovoltaic solar and wind power are preferable to both hydro and nuclear power, which are often heralded because they don’t emit carbon.

Most importantly, sound energy policy going forward requires that the energy-water nexus be taken into account as new sources of energy are developed and employed. Water and energy do mix and each new energy project proposal has to be measured against the water it is using. The default option whenever possible must be to develop photovoltaic solar and wind.