We now know that flight attendants hate when you order Diet Coke and other fizzy drinks on planes because they are hard to pour, which ultimately slows down service for everyone. Soda can also be pretty dehydrating.
So what should flyers be drinking instead?
It might not come as a huge shock that plain old water is the best thing to drink when flying, but you should always pay attention to where that water is coming from and adjust your order accordingly.
Why water is always a great choice
Water isn't just easy to pour, but it's really, really good for you. "The cabin air is dry and lacks moisture (it has very low humidity), so it's easier to become dehydrated," NBC News health and nutrition editor Madelyn Fernstrom told TODAY via email.
"Dehydration will make travelers more vulnerable to motion sickness, jet lag and headaches, which water can assist in treating before symptoms develop," Dr. Robert Quigley, senior vice president and regional medical director of International SOS and MedAire (a travel health and security risk mitigation company), added.
He advises travelers to drink about 250 milliliters (that's just over 1 cup) of water per hour when flying.
In addition to being hydrating, water is also the preferred beverage to serve by those pushing the cart. Flight attendant Dawn McGuckin-Fisher said, "Water is also best if you spill it —it's not sticky and doesn't stain!"
Be wary of tap water while flying
But not all water is created equal when it comes to what's available in the sky.
In 2004, the Environmental Protection Agency (EPA) found that 15% of aircrafts tested had tap water contaminated with disease-causing pathogens. Today, the Federal Drug Administration (FDA) and the Federal Aviation Administration (FAA) jointly monitor aircraft drinking water to ensure its safety.
In 2018, however, a study from the Hunter College NYC Food Policy Center still recommended that passengers avoid drinking tap water on planes because the water tanks that hold the liquid are not cleaned very often. "They're rarely fully emptied and probably cleaned every few years when the airplane goes in for its D-Checks or major overhaul check," Bobbie Laurie, a former flight attendant for US Airways and Virgin America who currently works for Jet Set TV, told TODAY.
While most airlines offer bottled water for drinking, coffee and tea are usually made from tap water, along with the plane's ice, so the study also advised avoiding those brewed beverages.
"To avoid the potential of contaminated water, travelers should always ask for non-carbonated bottled water, without ice, during the duration of their entire flight," said Quigley.
If you're not a fan of water, there are still healthful and hydrating options that won't totally annoy flight attendants. Fernstrom advised that bubbly, low-calorie drinks are another good option. "Try a splash of cranberry or orange juice in seltzer for extra flavor, or just add a slice of lemon or lime," she said. Ask for the can so you can control the ratio yourself.
McGuckin-Fisher suggested cutting sugary drinks for kids by adding water, too. "It cuts the sugar and hydrates them with water," she said.
And instead of waiting to board to get a drink, you can usually find plenty of refreshing options to take with you from the airport terminal. Coconut water is a hydrating option (just make sure it has no added sugar), as well as unsweetened bottled iced tea.
Besides Diet Coke, there are other drinks that nutrition experts recommend avoiding while flying.
Savory drinks like tomato juice and bloody Mary mix may seem to taste extra delicious in the air (Laurie said those were definitely passenger favorites when she was working as a flight attendant) due to the altitude impacting our taste buds. But these drinks can have lots of sodium, said Fernstrom, so she advised being mindful of your portions.
Fernstrom also said it's a good idea to limit alcohol to just one serving, since it's a diuretic that will accelerate the dehydration process. Quigley added that the decrease in pressure when flying can also enhance the negative effects of alcohol.
Should all caffeine be avoided?
Fernstrom said that while caffeine is a mild diuretic, a serving or two is not likely to cause any significant dehydration in healthy people. She recommended sticking with decaffeinated coffee or herbal teas if you're having more than a cup or two, which you can grab from the airport Starbucks to avoid drinking the questionable water.
And while many flight attendants definitely find Diet Coke frustrating to pour (McGuckin-Fisher said any drink that is not carbonated is easier), Quigley said the carbonation also isn't great for passengers' tummies. "A carbonated beverage in flight can exacerbate the increase in intestinal gas, which typically expands up to 30% due to the decrease in barometric pressure," he said. "This can result in bloating and nausea."
Want to keep flight attendants happy? Here's a tip: "My pet peeve is those who drink tomato juice then stuff their napkin and snack wrappers in the cup," McGuckin-Fisher said. "We recycle on the plane and you can't get the stuff out of the cup because it sticks to the sides."