WYSOX, Pa. - The Marcellus Shale natural gas industry has a huge thirst for water - to hydraulically fracture a single gas well requires upward of a thousand tanker-trucks of water.

And so during the summer, when some streams here in gas-rich northern Pennsylvania naturally turn into trickles, the Susquehanna River Basin Commission pays close attention to ensure that drilling interests don't suck the state's creeks dry.

The SRBC, an interstate agency responsible for managing the Susquehanna watershed, this summer has suspended withdrawals from as many as 40 permitted locations because of seasonal low flows. Most of the suspended locations affect gas drillers.

But the shale-gas industry, now moving rapidly from an exploratory to a production phase, has hardly missed a beat. Fracking continues, largely unabated.

The commission allows drillers to withdraw up to 98 million gallons per day at 142 locations, though in reality, the industry uses far less than what it is allowed, the SRBC says. The permitted amounts are based on elaborate computations tied to historical stream flows. When stream levels fall below a certain level, withdrawals must stop.

Anticipating the seasonal fluctuations, natural gas operators have built vast networks of impoundments - plastic-lined ponds - to store water from the rainy seasons.

"The natural gas industry is trying to capture some of the large spring flows because they know they can't take water all summer," said Paula Ballaron, the SRBC's manager of policy implementation and outreach.

But drillers can continue to pump water out of larger rivers even in the summer because the volumes the SRBC allows are small compared with the total flow.

Public confusion about where the drillers can legally withdraw water in the summer - and where it is banned - has caused an increase in complaints to the SRBC. The agency has three inspectors based in Sayre. They prowl the basin looking for violators.

"Since the drilling started, we get calls from some people who claim the river flows have never been lower than this," said Eric R. Roof, the commission's director of compliance. "People are very concerned."

Most complaints are unfounded, he said. Withdrawals that the public reports as suspicious turn out to be legal pumping by municipal road crews, garden centers, and nurseries that are allowed to withdraw small amounts of water. Gas drillers have sufficient, metered withdrawal points to meet their needs.

Complicated process

The business of withdrawing water is more complicated than simply inserting a hose into the river and pumping. The SRBC requires drillers to document and meter the withdrawals, and to pay for them.

Chesapeake Energy Corp., the state's largest driller and among the most active here in Bradford County, operates a withdrawal point on the Susquehanna River in Wysox that is unaffected by SRBC's dry-weather "passby" flow restrictions.

Chesapeake's pump station, drawing water from an intake buried on the riverbed, fills five towering 21,000-gallon tanks nearby, while a parade of trucks waits to fill up at four adjacent computer-controlled stations. It takes about 10 minutes to fill a 3,360-gallon tanker truck. Tractor-trailer tankers, which hold 4,620 gallons, take a little longer.

When the metered withdrawals reach the site's daily limit of about one million gallons - that's enough to fill more than 200 trucks - the system automatically shuts down until midnight.

The SRBC estimates that the industry, based on projected drilling, will need about 30 million gallons a day.

By comparison, suppliers of public water in the basin consume 325 million gallons a day, and power plants require 190 million gallons a day for coolant. A single nuclear reactor proposed in Luzerne County would require 30 million gallons of water a day.

"Power plants may draw much more water, but it's a stationary withdrawal, unseen by the public," said Brian Grove, Chesapeake's director of corporate development. Even recreational activities - watering golf courses and making snow at ski resorts - consume more water than natural gas production.

But until the industry finishes building freshwater pipeline networks to move water out of view to remote drilling sites, the industry is reliant upon thousands of tanker trucks to ferry water to their impoundments. And the truck traffic makes the industry's water consumption very visible indeed.

Chesapeake maintains 51 impoundments in the region that can hold up to 15 million gallons each, Grove said. A single impoundment might require 4,000 round trips to fill.

After a well is drilled, the hydraulic-fracturing procedure requires upward of five million gallons of water, which is injected under high pressure along with sand and additives to shatter the shale to release the natural gas. About 15 percent of the fluid returns to the surface immediately as wastewater, most of which, the SRBC says, is being recycled in new fracturing operations.

The regulators

The SRBC devised its gas-drilling regulations early in the Marcellus Shale boom, before opposition had organized. It was also unhindered by the politics that have stymied the Delaware River Basin Commission, whose area captures a far bigger population, including Philadelphia and its suburbs.

"If it's a sustainable withdrawal, we have no legal basis for denying it," said Susan Obleski, the SRBC's spokeswoman.

Gas drilling has been a boon for the SRBC, whose budget has doubled since 2007 to $10 million. Its fee income, mostly from gas-industry charges for drilling-site approvals and water withdrawals, has increased sixfold to $6.2 million.

The gas industry, meanwhile, has tapped into the commission's workforce. Chesapeake has hired two high-ranking SRBC officials, Michael G. Brownell and Jennifer L. Hoffman, to staff its regulatory-affairs office.

Some environmentalists are worried that drilling has moved forward more quickly than the agency's ability to understand its consequences, and they are concerned about what will happen when drilling expands into New York State, where the Susquehanna's tributaries are smaller and more sensitive.

"Nobody has done a build-out of what will happen when drilling is permitted in New York state, which will have a significant impact," said Katy Dunlap, the eastern water project director of Trout Unlimited Inc.

For SRBC inspectors such as Andrew J. Orsborn, the water withdrawals are taking on a routine.

When he was hired 18 months ago, Orsborn said, he looked forward to an adventurous life of sleuthing on the industry.

"When I first started, I thought, 'They've got to be cheating,' " said Orsborn, 30, who has a degree in a wildlife management. " 'I'm going to catch them now.' "

Despite conducting surprise inspections of water stations and drilling sites at nights and on weekends, and following a few water trucks clandestinely to confirm the legitimacy of their work, Orsborn said most violations he has found were minor - improper signage at well sites, or errors in paperwork.

"What I've found," he said, "is that they're mostly self-policing."