Got bubbles? Alarms have been ringing for months about the risk that natural gas drilling poses to drinking water supplies, but recent reports of water contamination just a few hours away have prompted representatives from New York City to once again appeal to the state government to ban drilling inside the watershed serving 9 million city residents.

In a report to be issued tomorrow, Manhattan Borough President Scott Stringer cites two dozen cases across the country where drilling pollution appears to pose a threat to public health. Most of those cases were originally documented in a series of stories by ProPublica.

At issue are plans to begin widespread drilling of the Marcellus Shale, a deeply buried gas-rich layer that underlies the southern part of New York state and Pennsylvania. The Marcellus is believed by some geologists to hold as much as 400 trillion cubic feet of recoverable gas, equal to 20 years of the United States' current total production, and its development could be worth $1 billion a year to New York's economy -- money that is desperately needed to fill Albany's gaping budget hole.

But much of the drilling would underlie the giant reservoirs and watershed that provides unfiltered drinking water to New York City. City officials have already protested that any pollution in the watershed could jeopardize the city's permit to provide unfiltered water and force it to build a $10 billion water treatment plant. Now Stringer says he's concerned the state -- which has not held any of its public hearings on the issue in New York City -- may drive forward regardless.

"We can't allow those pressures to push us into hasty decisions that come at the cost of New Yorkers' health -- or the state's long-term interests," Stringer said in a statement issued with the report.

ProPublica's investigations have shown that the state has done little to study the impacts drilling might have on water supplies and is unprepared to treat the copious amounts of waste water it produces.

Most concerning are a suite of chemicals used in the key process of hydraulic fracturing, where millions of gallons of fluids are pumped underground at extremely high pressure to break up the rock and release the gas. The identities of some of the chemicals are protected trade information that has never been released to governments or to the public, but which are believed to be highly toxic.

Scientists have had difficulty measuring any threat because they can't trace the source of pollution without knowing the names of the chemicals used in fracturing. It is also unclear whether any of the water treatment facilities in New York and Pennsylvania, the heart of the Marcellus deposit, are capable of cleaning the waste before it is released back into the region's rivers and lakes.