Federal regulators have issued final rules that require air carriers to test the tap water served to passengers and crew and used in plane lavatories in an attempt to avoid bacteria contamination of onboard water. The Environmental Protection Agency (EPA) rules set out schedules for how frequently airlines must flush and disinfect the water systems on planes and test for bacteria.

Five years ago, the EPA determined that airlines weren't adhering to drinking water regulations. The federal agency tested water from 327 planes, of which 15 percent tested positive for coliform. The EPA said about 20 percent of the water tested didn't show any amount of chlorine, an indication it had not been treated.

Forty-five U.S. airlines have already agreed to monitor their tap water quality and publicly report the results under a settlement with EPA. The new rule gives air carriers up to two years to comply with the new schedules. The EPA estimates the cost of the new regulation at $7 million a year, or about a penny per ticket.

"This rule is a significant step forward in protecting people's health when they travel," said Peter Silva, assistant administrator for EPA's Office of Water. "EPA has taken this step to make sure the public has drinking water that meets standards, both in the air and on the ground."

EPA said "the aircraft drinking water rule tailors existing health-based drinking water regulations to fit the unique characteristics of aircraft public water systems."

The rule applies to the aircraft's onboard water system only. The Food and Drug Administration (FDA) is responsible for regulating the airport watering points that include the water cabinets, carts, trucks, and hoses from which aircraft board water. EPA and the states are responsible for regulating the public water systems that supply drinking water to the airport watering points.

The rule only applies to commercial transports under U.S. jurisdiction; however, EPA supports an international effort led by the World Health Organization (WHO) to develop international guidelines for aircraft drinking water.