Both candidates for the Democratic U.S. presidential nomination said they do not support the drilling practice behind the shale oil and gas boom.

Former U.S. Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders held a debate in Flint, Mich., Sunday night, moderated by CNN. Flint has been plagued by contaminated drinking water since state-appointed emergency managers in 2014 switched the supply to the Flint River, which caused lead to leach out of pipeline infrastructure because of its corrosive nature.

On broader health issues related to the environment, both candidates said their platforms offered the best opportunity to combat climate change. On issues related to the energy sector, Clinton offered conditions ranging from public support to the disclosure of chemicals used in hydraulic fracturing fluid before she'd support the drilling practice as a U.S. president.

"By the time we get through all of my conditions, I do not think there will be many places in America where fracking will continue to take place," she said. "I think that's the best approach, because right now, there are places where fracking is going on where it's not sufficiently regulated."

Clinton, who served as a senator in New York, which moved in opposition to the drilling practice known more commonly as fracking, said tightening regulations on the oil and gas sector would top her energy sector concerns as president.

"My answer is a lot shorter," the Vermont senator said. "I do not support fracking."

Vermont was the first state to ban fracking.

The drilling practice has been criticized for its possible link to minor earthquakes and the potential to contaminate groundwater supplies.

Both New York and Vermont have potential shale reserves, with New York hosting a portion of the Marcellus gas basin. Vermont has shale reserves near Lake Champlain, though a state report last year found tourism business interests trump any potential gains from energy.

According to campaign finance watchdog OpenSecrets.org, Clinton took in about $260,000 out of a total of $130 million in support from the oil and gas industry as of Feb. 22. Sanders took in $35,000 against a $96.3 million total for the campaign.