The U.S. government has found for the second time in recent months that water from a sampling of commercial aircraft galleys and bathrooms was not safe for use, regulators said on Wednesday.

Tests last November and December by the Environmental Protection Agency on a fraction of the thousands of planes in the domestic and international commercial fleet found samples failed to meet government drinking water standards.

The EPA said the results of the latest testing showed the scope of the problem and reinforced the agency’s decision to forge agreements with airlines to more closely monitor water systems and tighten sanitary measures.

The agreements, which include testing protocols, are not fully in place yet. They will govern drinking water safety until new regulations are devised.

The EPA again warned that passengers with compromised immune systems or others who are concerned about water quality “may want to request” canned or bottled beverages and refrain from coffee or tea unless made with bottled water.

The biggest domestic airlines again questioned the government’s sampling results and countered that their water is safe.

Tests last summer found that 12 percent of 158 randomly selected aircraft operated by domestic and international carriers tested positive for coliform bacteria, which by itself may not pose a health risk. But coliform bacteria in drinking water indicates that other disease-causing organisms, or pathogens, may be present.

Water on two planes tested last summer contained E.coli, a potentially deadly bacteria commonly associated with food poisoning.

At the time, EPA officials called the results surprising and moved to alert the public, negotiate water testing agreements with major carriers, and launch a second-round of sampling.

The latest tests last fall found that water on 17 percent of 169 randomly selected planes was positive for coliform. E. coli was not found in any samples this time, the EPA said. The airlines were not identified.

The latest tests evaluated samples from galleys and bathrooms of each plane. The initial analysis was not similarly controlled. Most of the positive samples from the second test came from aircraft bathrooms, the EPA said.

An airline industry group, the Air Transport Association, pointed out the new results produced no positive results for E. coli and called the agency’s testing methods outdated.

“Once again, the EPA chose to include samples from aircraft lavatories, which are essentially public restrooms, where there’s a high potential for cross-contamination of samples,” said Nancy Young, the association’s managing director of environmental programs and associate general counsel.

The trade group also said that airline drinking water comes from municipal supplies and that no government agency has reported any illness from water aboard commercial planes.

Most domestic airlines serve bottled water on their flights.