All of Long Island’s drinking water comes from the ground beneath our feet, but experts say generations of living, working and playing on the Island has endangered the water quality.

Long Island is one of only 12 places in the U.S. designated by the federal government as a sole-source aquifer. Decades of industrial development and factories, chemical plants and dry cleaners have taken their toll on the quality of the groundwater.

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"Where that local dry cleaners, for example, was dumping their waste outside because it was acceptable back then... that one little dry cleaner has contaminated millions of gallons of water," explains Dennis Kelleher, president of engineering firm H2M.

At the former Grumman plant in Bethpage, years of air and space projects left behind chemical waste. And New York's list of Superfund sites has a disproportionate number of hot spots on Long Island – there are more than 200 state and federally designated sites.

The issue of water quality now has the attention of public officials and residents.

"The public is understandably concerned when they hear about a contamination problem," says DEC Commissioner Basil Seggos. "But the state, federal and local agencies are working, all in the same direction, to fix this problem."

Solutions are not easy, or cheap. Cleaning up the Grumman plume alone will require an estimated $30 million to $50 million over the course of 35 to 50 years, according to Oyster Bay Supervisor Joe Saladino.

In addition to toxic plumes, antiquated cesspool systems allow dangerous levels of nitrogen to seep into Long Island's groundwater. About 30 percent of homes in Nassau still have cesspools, and in Suffolk, the number is closer to 80 percent. It's something Suffolk County Executive Steve Bellone says needs to change.

"This is an issue that no one municipality can handle, but we’ve all got to be part of the solution," Bellone says.

Environmentalists argue that continued protection of open spaces is vital to protecting our drinking water supply. Additionally, Suffolk County now offers grant money to homeowners to upgrade their septic systems.

Still, environmentalists warn the issue is one that Long Island will face well into the future.