Deroy Murdock has published an article entitled “Greener than ‘green’” in the National Review that compares several environmental impacts of fracking with those for several popular renewable energy sources. I strongly recommend the article.
Just one area of interest is the amount of water used per unit energy. Mr. Murdock claims it typically takes three gallons of water per million Btu of energy from fracking natural gas as compared with 11 gallons for nuclear power, 23 gallons for coal, and 15,800 gallons for corn ethanol.
The article is worth the read.