Most of America’s enormous natural gas reserves were inaccessible until Halliburton devised an extraction method called hydraulic fracturing, or “fracking.” This engineering miracle involves injecting zillions of gallons of “fracking liquid” deep into the ground, and this stuff ain’t rosewater. Directed by Josh Fox, this muckraking documentary is terrifying but also very entertaining, raising good questions about the ecological implications of the process and the political maneuvering that seems to have exempted its practitioners from normal environmental accountability. Fox’s populist-hippie-naïf shtick can be a bit much, but it’s hard not to like the guy (which is more than I can say about Michael Moore). That goes double for the beleaguered landowners he interviews, whose once-pristine well water now has an unfortunate tendency to burst into flame.