Residents of Quantico and the Marine Corps Base have been instructed to stop drinking tap water after inspectors found that the area's supplies are infested with bacteria.

Routine samples taken last month revealed that the water contained unacceptable levels of E. coli and fecal coliform bacteria.

Drinking the contaminated water could lead to diarrhea, nausea, vomiting, headaches, cramps or other ailments. Thus, officials have instructed residents to bring all drinking and cooking water to a rolling boil for at least one minute before using it, as is mandated by a state advisory. Residents are not at risk of becoming ill if they shower or bathe in the water.

So far, there have been no reported incidences of infection on the base or in town.

On the Marine Corps base, where the outbreak is affecting the 7,000 residents who live east of Interstate 95, officials are providing water at the self-service store.

"We're distributing bottled water free of charge," said Capt. Sean Clements, a base spokesman. "That situation may change. It'll be quite expensive after a while. . . . As of Thursday, we've bought 30,000 gallons" for residents.

At the same time, officials are vigorously trying to determine the cause of the contamination. The base's water treatment facility tested negative, Clements said, so they think the problem is somewhere in the distribution system. One hundred water samples were taken Thursday, and officials hope to learn more from those.

After the cause of the contamination is learned and the problem is addressed, the water will have to test negative three consecutive times for the advisory to be lifted.

The town of Quantico also is trying to determine the source of the contamination, but its water has tested negative twice so the advisory could be lifted there as soon as this afternoon.

"Everything seems to be going pretty good," said Mayor Mitchel Raftelis. "We have to wait for one more sample in 10 places. Yesterday, everything tested clear."