INDIANAPOLIS - Over the past month, Indiana has cited four gas stations after finding water in fuel stored in their underground storage tanks (USTs), the Indianapolis Star reports.

The number is surprising in that the state agency responsible for monitoring fuel has cited only five stations in the previous two years.

The citations stemmed from investigations that were triggered after several consumers complained of experiencing engine trouble in their vehicles.

State authorities have not identified the source of contamination, saying only that rain or snow can enter tanks when they are open for refilling, but they have not ruled out other causes.

"In my estimation, it's just a poor maintenance," said Larry Stump, director of the fuel inspection program at the Indiana State Department of Health, adding that there exists no evidence that station owners deliberately diluted their product.

Indeed, Scot Imus, executive director of the Petroleum Marketers and Convenience Store Association, said stores have no reason to shortchange customers.

"It's just an unfortunate situation that happens infrequently," Imus said. "Like anything that's mechanical, there can be hiccups in the system, and those can be addressed."

Indiana's Department of Health requires stations with water in their fuel to close until the problem is resolved.