If you’ve ever taken a red-eye flight, you’ve probably had a few cups of airline coffee. It’s not the best-tasting brew, but hey, it’s coffee—how bad could it be? 
Pretty bad, apparently. Some airline crew members say that they wouldn’t ever consider drinking the coffee or tea that they serve to their passengers, according to a report from Business Insider. “Flight attendants will not drink hot water on the plane,” a flight attendant allegedly told the website. “They will not drink plain coffee, and they will not drink plain tea.” 
Their objections have nothing to do with the flavor of the java. Apparently, hot water comes directly from the planes’ taps, and those taps are downright disgusting.
Data from the Environmental Protection Agency (EPA) backs up that claim, to a degree.
In 2004, the EPA tested drinking water from 158 randomly selected passenger airplanes. “Preliminary data released by EPA today shows that in the recent tests, most of the aircraft tested (87.4%) met EPA drinking water quality standards,” the agency wrote in a press release accompanying the revelations. “However, 12.6 percent of domestic and international passenger aircraft tested in the U.S. carried water that did not meet EPA standards.” 
Those planes’ samples contain coliform, a broad class of bacteria that can potentially cause disease. Coliform often comes from human or animal feces (try not to think too hard about that). Additionally, two planes’ tap water supply tested positive for E. coli, a common type of coliform bacterium that can cause severe fevers, gastric distress, and other medically significant symptoms.
Many planes didn’t meet the standards because they store their tap water in tanks that are rarely cleaned.
NBC reports that the coliform bacteria is probably present in delivery trucks. When the tanks are transferred to the planes, some of the bacteria goes with them and then develops into colonies over time. 
“Passengers with compromised immune systems or others concerned may want to request canned or bottled beverages,” the EPA noted, adding that officials had been working with the Air Transport Association (ATA) since 2002 to reform water standards on planes. The press release also notes that the EPA would consider legal action if airlines weren’t able to agree on effective methods for improving their standards.
Years later, little had changed.
The EPA ran another test in 2012 and found that 12 percent of randomly selected planes tested positive for coliform, according to NBC 5. That wasn’t a significant improvement from the 2008 test. 
Some of the tested planes also tested positive for E. coli, although again, this dangerous bacterium was only present in a small number of aircraft. Flight attendant organizations claim that they’ve been pushing for better standards for years. “Water onboard is regulated under the Environmental Protection Agency to ensure safe drinking water on the aircraft,” the The Association of Flight Attendants-CWA, told Business Insider. “The Association of Flight Attendants-CWA pushed for this regulation over 15 years ago. The regulation gives broad discretion to airlines on how often they must test the water and flush the tanks. AFA does not believe this regulation goes far enough or is sufficiently enforced.” The airlines, of course, disagreed. While most refused to comment directly, Airlines for America, a group that represents several major airlines, issued a statement. 
“The safety of our passengers and crew remain the airlines’ primary focus, including the provision of clean drinking water,” the statement read. “To meet customer preferences, airlines typically provide bottled water while also ensuring water available through the aircraft onboard water systems is safe. Airlines work closely with the Environmental Protection Agency to ensure that water received from municipalities for onboard systems is safe and to maintain that safety by following rigorous sampling and management requirements once received.” Even so, the numbers don’t lie, and the EPA’s research doesn’t seem to support the idea that current regulations are effective. For the time being, that seems unlikely to change.
If you fly regularly, here’s what you need to know.
First of all, understand that there’s a limited risk for healthy individuals. While the idea of coliform in your drinking water is disgusting, the classification is broad enough that the mere presence of coliform bacteria doesn’t pose an immediate health risk. Obviously, this isn’t the case with E. coli, but that was limited to a very small percentage of planes. The issue only affects water that comes directly out of the planes’ taps, so if you order cold water, you’re probably safe—you’ll typically get your drinking water from a bottle. 
If your immune system is compromised, however, you may want to follow the EPA’s recommendations and specifically request bottled drinks. Although water is heated considerably to brew tea and coffee, the brewing process doesn’t do enough to eliminate microorganisms, according to experts. Heating “might kill some of the organisms—the more susceptible ones—but it’s not going to kill the majority of them,” environmental scientist Brenda Wiles told NBC 5. Mothers should also avoid filling babies’ bottles with airplane tap water. “That doesn’t sound like a very good idea,” Dr. Cedric Spak of the Baylor University Medical Center told NBC. 
As for those red-eye flights, passengers should probably wait until they touch down before grabbing a cup of coffee. After all, every major airport has multiple coffee shops—and if you see a flight attendant at one of those shops, don’t be surprised.
