Our investigation into water on airplanes will make you think before you drink.

"Don't drink the water" may be the world's oldest travel advice--once you've arrived somewhere. But how safe is it to drink the water en route?A random sampling by Travel & Leisure found that the quality of water on airplanes isn't always as safe as you might think (see Weighing the Waters, below).

"Problems with airlines are not uncommon," says a spokesperson at the Food and Drug Administration's San Francisco office. "A number of warning letters have been issued this year for violations of the Public Health Service Act." Although she adds that "most of the warnings involve food service, not potable water," in July her office cited Honolulu International Airport when fecal coliform bacteria was discovered in the water system used to fill tanks on Aloha Airlines and Hawaiian Air flights. (The airport was also cited in 1991.)

The problem is not confined to Honolulu. In 1993, a cryptosporidium outbreak in Milwaukee's water supply made 403,000 people sick and resulted in 100 deaths. Based on anecdotal reports, the Centers for Disease Control believes planes that landed there took on contaminated water, which air travelers then ingested. A 1994 cryptosporidium outbreak in Las Vegas was not confirmed until four months after it began--airplanes may have taken on contaminated water there as well.

Even more alarming is the fact that travelers who never set foot in Milwaukee or Las Vegas could easily have been affected. "All these conveyances move around and take water from many sources," says David Hajduk, an environmental health engineer at the FDA. The CDC has no confirmed reports of anyone getting sick from drinking tainted water on airplanes, but collecting such statistics is almost impossible. "Outbreaks of gastrointestinal illness are difficult to find," says CDC epidemiologist Bill Mackenzie. "People drink the water and get off the plane and disperse."

The above incidents involved domestic water supplies, which are heavily regulated by states and the federal government. On international flights, however, there's no federal oversight at all. "That's not under our jurisdiction," says Steve Clark of the Environmental Protection Agency. "I would hope that the airlines are overseeing the water." Although some airports have their own purification systems, in many countries where planes fill their tanks the quality of the water is dubious at best. The FDA seems to be of two minds. The agency's Larry Edwards says, "We basically trust that other countries are conducting a similar program" of monitoring water safety. Hajduk remarks, "If I were flying in a Third World country, I'd drink bottled water."

Many airlines have responded to the public's concerns by offering only bottled water. Some, however, serve water from the plane's tanks. Northwest and Continental, for example, provide both bottled and tap water. A spokesperson for American claimed that the airline serves only bottled water; but Emily Carter, the head of the health department of the Association of Professional Flight Attendants, a union at American, informed us that most of the water served on American's flights--including water used to make ice and coffee-- comes from the water tanks. "We fill our tanks in other countries, and that has been an issue," she says. "There are some places I'd be cautious about." A few airlines even use a caste system to decide who gets bottled water. China Airlines, for example, offers it only in first and business class. On international routes United serves it to first- and business-class passengers but only occasionally in coach.

Whether airlines provide bottled water or not, the lavatory tap water-- which passengers might ingest, say, while brushing their teeth-- is by law supposed to be potable. Airlines are subject to spot checks by the FDA (responsible for water transported on airplanes) and the EPA (which sets water-quality standards, leaving it up to local agencies to monitor the water supply). "We inspect the watering points about once every three years, and on the conveyances if there's a complaint or a problem," says an FDA spokesperson. "The industry itself is responsible," insists the EPA's Clark. "This is not something we've spent a whole lot of time on." Unfortunately, some airlines don't do much testing, either. Continental and Northwest test water at the source but not on planes, where bacteria can grow in the tanks. A spokesperson at United said the airline does not conduct any regular tests itself-- but the only way the FDA is going to test it is if there is a complaint.

What exactly would the tests be for?The most common method to determine water potability is a total coliform test, which measures the amount of coliform bacteria. Some types of fecal coliform (that is, coliform from human and animal waste), such as E. coli, can cause severe diarrhea, cramps, and nausea, and can be deadly to anyone with a suppressed immune system (such as children, the elderly, and people with HIV). While other types of coliform do not themselves make people sick, they are good indicators for the presence of dangerous pathogens that cause such diseases as typhoid fever, gastroenteritis, and hepatitis A. Water that contains an abnormally high coliform count is considered unsafe to drink.

Coliform is usually killed by chlorination, but cryptosporidium is one of several parasites that are resistant to chlorination and must be filtered out. United and Continental are among the airlines that filter their water. Though usually effective, filtering is not foolproof because cryptosporidium parasites are so small. "Milwaukee and Las Vegas have filtered-water utilities," says the CDC's Mackenzie. "It doesn't always work." Testing for cryptosporidium is inordinately expensive, so it's not done routinely. Outbreaks are detected only when a significant number of people get sick, which means it could be several months before the public is alerted.

In addition to testing for bacteria, municipalities routinely test for dangerous chemicals, which are not likely to enter water during its transfer to the aircraft. But according to Jane Houlihan of the Environmental Working Group, a watchdog organization, domestic water supplies may be less safe than European water when it comes to most chemicals. She says that contrary to popular belief, U.S. drinking-water standards are more lax than European Union standards for 45 of 64 chemicals. U.S. and European standards for bacteria and parasites are similar, she says, although "in Europe a different disinfection method-- ozonation-- is much more popular. It's more effective at disarming cryptosporidium." Most treatment plants in the United States do not employ ozonation-- in which ozone is used instead of chlorine-- because they find it too expensive to switch systems.

None of this means you shouldn't drink water during your next flight. In fact, the pressurized cabin atmosphere leaves you susceptible to dehydration, so you should drink as much water as possible. But to be on the safe side, take the same precautions you would about drinking water in a foreign country-- even if you're flying in the United States. Drink only bottled water, and avoid ice and tap water-- whether from the lavatories or served by the flight attendants. If you're given bottled water, check to make sure the label bears the seal of the NSF (the National Sanitation Foundation). (Of course, you can also bring your own bottled water.) And if you have a suppressed immune system, be extra vigilant. Ultimately, the likelihood of contracting a serious illness from airplane drinking water is probably remote, but it's better to be safe than sick.

Of the four airlines we tested, one failed

While far from authoritative, a Travel & Leisure test of airplane water proved that clean water isn't necessarily where you'd expect it. Using sterilized containers provided by Ambient Labs, New York, we took in-flight samples-- of the water served to passengers, used to make ice, and from the lavatory tap-- from four airlines: Continental, US Airways, Mexicana, and KLM. Ambient Labs then tested it for coliform bacteria to determine whether the water was potable. The good news: all the water and ice served in the cabins came back clean. The bad news: KLM's lavatory water tested positive for coliform. "The concentrations of all parameters analyzed," read the lab report, "fall above the maximum contaminant levels stipulated in the National Primary and Secondary Drinking Water Regulations pursuant to the federal Safe Drinking Water Act, indicating that, with regard to these elements, the water is chemically unfit for human consumption." KLM spokesperson Hans Leijt was surprised by the results. "Bear in mind," he points out, "we empty and refill our tanks every twenty-four hours. On intercontinental flights we empty them after every flight. And we test the water regularly."

The rail company randomly tests about 100 of its 1,323 passenger cars per month. So far this year, approximately 10 samples have tested positive for coliform (in T&L's test, the samples were negative). "Ten is not a number we want," says Amtrak's assistant director of public health, Victor Zare, "but it's not unusually high. They were isolated incidents with no consistency-- it could have been the lab, the sampler, the faucet. If there was consistency, we'd do some sort of follow-up action." In November 1997, the testing did uncover a problem: fecal coliform was found in the drinking water of 17 rail cars that had obtained water in Miami. Despite an investigation by outside consultants, the cause was never determined. "If you ask the city of Miami, they say it wasn't them, and we say it wasn't us," Zare says. There were no reports of anyone becoming ill before the problem was caught.