Some part-time South Fork residents are using millions of gallons more water a year than the average full-time household, a News 12 Long Island investigation has found.

The average Suffolk County home uses around 120,000 gallons of water a year, officials say. But according to the Suffolk County Water Authority, a handful of homes, mostly on the South Fork, use 50 to 100 times that amount -- and they are a major drain on the local aquifer system.

One home alone used more than 22 million gallons of water last year, according to officials.

"I would say, if we don't get a change [in] perhaps 10 years or earlier, it could be a crisis," says Jim Gaughran, of the Water Authority. "People that use that much water when it's a single residential home are the people that are taxing our supply significantly."

Through a Freedom of Information Law request, News 12 obtained the names of some of the county's biggest water users. They include the billionaire industrialist David Koch, who used the 22 million gallons, music producer David Geffen, who used more than 6 million gallons, and investment mogul Andrew Zaro, who used more than 10 million gallons.

Environmental activists say that excessive overuse of water can lead to salt water infiltration of Long Island's aquifers and contamination of drinking water.

"As these water hogs use more and more water, withdrawing, creating a drawdown in our water levels, they're actually causing plumes to move and migrate more rapidly," says Adrienne Esposito, of Citizens Campaign for the Environment.

To deal with the heavy usage on the East End, the Water Authority spent $20 million to upgrade its public well system by adding additional wells and enlarging pipes. Officials say the cost of those upgrades was spread among all customers, not just the people who use them.

The added cost isn't sitting well with some residents, who say they used to pay around $20 for water, and now shell out more than $100.

The Water Authority says it doesn't currently have the legal power to force the top water users to cut back. Assemblyman Fred Thiele says it may be necessary to change that in the future -- but for now he says it's everyone's responsibility to conserve.

"I think we need to change habits now and behaviors now, before we get to the point where we have to impact everybody with mandatory restrictions," Thiele says.

News 12 attempted to ask about the water usage at the Koch residence, but was turned away.