The country's push to find clean domestic energy has zeroed in on natural gas, but cases of water contamination have raised serious questions about the primary drilling method being used.

Vast deposits of natural gas, large enough to supply the country for decades, have brought a drilling boom stretching across 31 states. The drilling technique being used, called hydraulic fracturing, shoots water, sand and toxic chemicals into the ground to break up rock and release the gas. The Environmental Protection Agency has declared the process to be safe, but water contamination has been reported in more than a thousand places where drilling is happening. Gas companies, exempt from federal laws protecting water supplies, may conceal the identities of their chemicals as trade secrets, making it difficult to determine the cause of contamination.

The EPA is now conducting a deeper study of the drilling, New York state has blocked drilling in New York City’s watershed, and lawmakers are pushing for closer oversight of the industry. The industry -- in the form of millions of dollars spent on lobbying, a slew of court cases, and a robust public relations campaign -- is pushing back.