Gut Check: Should You Drink Coffee or Tea on an Airplane?

Warnings about the water used to make tea and coffee on airplanes have been resurfacing on TikTok — but is it really unsafe to drink water from a plane’s water tanks?

Some of the videos are hosted by people who claim to be flight attendants who steer clear of nonbottled or canned beverages on flights due to concerns with how often — or not — on-board water tanks are cleaned.

The issue was originally stirred up by a analysis released in 2019 by researchers at CUNY's Hunter College that looked at water safety data for water served to passengers on 11 major airlines in the United States. The study ranked 10 major and 13 regional airlines by the quality of water provided onboard flights. At the time of the study, nearly all regional airlines were found to violate the Environmental Protection Agency's (EPA) Aircraft Drinking Water Rule, a 2011 law that requires airlines to provide flight staff and passengers with safe drinking water. The law requires airlines to disinfect and flush each plane’s water tank four times a year. They can also choose to disinfect and flush the tanks just once a year, but in those cases, the airline is required to test the water for potentially harmful microbes, including E. coli, monthly.

A year after the law went into effect, violations dropped by nearly 70 percent, though the drop in violations could be due to the EPA's reluctance to issue citations, the researchers noted.

Today, reported samples taken from different airlines and any violations can be seen by the public in EPA compliance reports published online. So if there is a violation, the public can know about it.

To be extra safe, the CUNY researchers advised people never to drink water onboard a plane that does not come from a sealed bottle. They also said passengers should not drink coffee or tea brewed on their flight, and that they should even use hand sanitizer instead of washing their hands with onboard water.

There’s a ick factor to knowing how often airlines are legally required to clean aircraft water tanks, but drinking nonbottled water on a flight is not a likely source of gastrointestinal (GI) issues while traveling, says Kyle Staller, MD, MPH, director of the Gastrointestinal Motility Laboratory at Massachusetts General Hospital and assistant professor at Harvard Medical School in Boston.

“That fear is probably mislaid because the water on airplane tanks is changed and it’s heated, which would kill the bacteria,” Dr. Staller says.

Regardless of what you drink, it’is important to pay attention to what you’re drinking while flying and make sure you aren’t getting dehydrated or throwing off the rhythms your body is used to. According to a study published in 2020 in the journal Nutrients, it’s easier to get dehydrated while flying than it is on the ground, especially on long flights. Some evidence suggests that being in an environment with lower pressure than sea level, in addition to being exposed to dry, cold circulating air, can cause fluid to shift in the body, which could accelerate dehydration.

You may also not be drinking enough water to begin with.

“Generally you aren’t drinking enough water on a plane because you’re drinking from those small little cups they serve you. Also the cabin is dry, so you’re losing moisture by just breathing that dry cabin air,” Staller says. It’s always a good idea to bring a reusable water bottle through airport security and fill it up before you board the plane.

People are also often drinking caffeine or alcohol. Both are diuretics that increase urine production, which flushes water from the body faster, though most research suggests that the water in caffeinated beverages such as tea and coffee make up for its diuretic effects, according to Mayo Clinic.

According to a review published in 2022 in the journal Nutrients, coffee increases stomach acid, which can cause Gi issues such as acid reflux or even stomach ulcers, especially when people drink coffee on an empty stomach. But this isn’t the case for everyone and the research has turned up mixed conclusions. According to the Centers for Disease Control and Prevention (CDC), moderate caffeine consumption, up to 400 milligrams per day, or about three to five cups of coffee, is fine for most people, and around 80 percent of adults in the United States drink caffeinated beverages, including coffee, every day, per the CDC.

However, alcohol is something Staller recommends staying away from while flying. A survey by the flight booking company Cheap Flights found that between 43 and 53 percent of travelers, depending where they’re from, drink while traveling via airplane. Almost 30 percent said they’ve had their first drink before noon while on vacation, while almost 40 percent admit they drink earlier than usual on days they’re flying. Six percent had their first drink by 8 a.m.

“There are few other places where people are drinking in the morning and some of that is self-treatment of flight anxiety. The danger is not only are you throwing off your schedule, but you are dehydrating yourself,” he says.

Most of the research on how alcohol affects the gut has studied people who have chronic alcohol use, rather than those who consume it casually or occasionally, such as while traveling.

But it is dehydrating, and if someone is drinking, they may also find themselves in a cycle of counteracting the effects of alcohol with excess caffeine while traveling.

Time Zone Changes Can Disturb the Gut

A far more likely source of GI disturbances during long-distance travel is dropping your body into a new time zone and, in the case of early or late flights, being awake at odd hours, Staller says.

“Your gut has a circadian rhythm — a time clock — just like the rest of you,” he says. “Just like you may feel a bit off while traveling, your gut will, too.”

During sleep, the colon is “pretty quiet,” Staller says. As soon as a person wakes up, the colon starts to contract, which is why most people experience a morning bowel movement, he adds.

Food also activates colon contractions.

“When you’re eating at different times during a flight or once you land, that can cause constipation and indigestion,” says Staller.

Changes in what we’re eating can also cause GI upset during travel.

“Most of us tend to eat mostly the same foods if we are in the same environment, but if you uproot us, we may eat things that are unfamiliar to our gut and challenging to our system,” Staller says.

He recommends taking a fiber supplement to help re-regulate the gut while traveling if you know you’re someone who gets constipated. But always try the supplements at home first. “It’s not that they are dangerous, but they can cause bloating,” he says. And remember to stay hydrated, because taking a fiber supplement without liquid is akin to not doing anything at all.

You should also be more cautious of water if you’re traveling internationally. Potentially unsafe tap water may be used to make ice cubes or wash vegetables and dishes in some countries.

“That can lead to the spectrum of GI bugs, most of the time that cause diarrhea,” Staller says.

Some may cause more serious issues, such as bloody stool and a high fever, which requires an immediate visit to a health care provider, he says; “At a minimum they can be dehydrating, which is the most dangerous part of diarrhea.”

However, “unless you don’t enjoy the local culture, it’s hard to be completely impervious to those things,” he says.