When championing any given cause, it's not always easy to be completely objective about it. Sometimes, we can even be blind to facts that run counter to our perceptions. Scientists, though, try never to shy away from the truth, even (perhaps especially) when it is inconvenient. To be proven wrong isn't a failure — instead it is a step toward a more complete view of the problem one is trying to solve. Keep this in mind as you read the following sentences.
A lifecycle analysis (LCA) by researchers at the Argonne National Laboratory of various alternative fuels shows that they consume more water than fossil fuels. In a paper published in Energy & Environmental Science, they compare the amount of water used per unit of energy and kilometer traveled. It compares gasoline, diesel, natural gas, electricity from various sources, biodiesel, ethanol, and hydrogen from various sources.
There is a trade off in every proposed solution to environmental problems we face.
Electricity provided the bookends for water usage, with wind power using the least (one liter per km) and hydropower affecting water the most (19,185 L/km, moistly through reservoir evaporation). CNG (59 L/km) was also very low on water use, followed by diesel (154 L/km), gasoline (166 L/km), and electricity from natural gas (284 L/km). Biodiesel (2,424 L/km) and ethanol (1,933 L/km) consume the most water throughout their lifecycle after hydroelectricity. Compressed hydrogen is in the middle of the pack, ranging from 400 to 496 L/km depending on the source. Coal electricity uses 659 L/km, while nuclear power uses 779 L/km.
While water consumption is just one aspect by which to measure one particular fuel against another, the results from this LCA study serve as a reminder that there is a trade off in every proposed solution to environmental problems we face. And of course, this study is limited in its scope. It doesn't show how capturing fossil fuels affects water quality, for instance, just its consumption. Certainly, there are much worse things we can do to the environment than consume water, which is why we look to alternatives to fossil fuels in the first place. We just need to be vigilant about our awareness of the consequences, minimize the undesired effects and try to weigh them to achieve the greatest net benefit. The advantages of alternative fuels are numerous, and if we can improve the amount of water they use, all the better.