Turning coal into gasoline requires water
Technologies exist for converting coal into gasoline, diesel, and jet fuels, which makes coal of interest for helping to meet US transportation fuels needs, since the US is rich in coal. But making and using liquids from coal can produce more CO2 than just using petroleum fuels. And there is also a question of water, which is especially relevant for the American West. The West has lots of coal, especially in Wyoming and Montana — but not so much water. Climate change and population growth have been diminishing regional water availability (in western streams and due to early snowmelt, for example) and threaten to make future drought problems worse.
That being the case, any new demands on water, beyond the already-competing interests of population, agriculture and ecosystems, are likely to make matters even more strained. The conversion of coal into liquid fuels, such as gasoline or diesel, would be one such demand. It is estimated that coal-to-liquid conversion will require between one and five gallons of water for every gallon of fuel produced.[[Western Governors' Association. “Coal-To-Liquids, 2007.” (PDF)]]
The actual number will depend upon the specific technologies adopted for the conversion process.