Fountain — named for a creek that once gave life to this southern Colorado town — is now part of a growing list of American communities dealing with elevated levels of perfluorinated chemicals, or PFCs, in their drinking water. In the last few months, PFC poisoning has upended municipalities around the country, including Hoosick Falls, N.Y., home to a plastics factory, and North Bennington, Vt., once home to a chemical plant.

Unlike in many of the other places, the contamination in Fountain and in two nearby communities, Widefield and Security, is not believed to be related to manufacturing. Rather, the authorities suspect that it was caused by Aqueous Film Forming Foam, a firefighting substance used on military bases nationwide.

Defense Department officials initially identified about 700 sites of possible contamination, but that number has surged to at least 2,000, most of them on Air Force bases, said Mark A. Correll, a deputy assistant secretary for environment, safety and infrastructure at the Air Force.

All of the nine bases that the Air Force has examined so far had higher-than-recommended levels of PFCs in the local drinking water. Four bases identified by the Navy were also found to have contaminated water. In some places, the contamination affects one household. In others, it affects thousands of people.