It turns out, you might be ordering some of the dirtiest beverages in the skies. 

You’ve likely heard that brushing your teeth at 10,000 feet with tap water from the airplane bathroom isn’t advised–namely because the water tanks on planes are almost never cleaned, and beyond that, they’re located right beside the lavatories on every flight. 

For this reason, airline professionals stress the importance of carrying a bottle (or two) of filtered water or asking for one on the plane. Studies indicate that the average person should be consuming 8 ounces of water per hour on each flight–in other words, it might be worth bringing a few water bottles in case you can’t get a hold of your flight attendant every hour. 

Coffee and tea on flights are always made using the airplane’s onboard water supply–these are the two beverages to be extra wary of, according to a TikTok video posted by former flight attendant Kat Kamalani. 

Even worse? The coffee machines and pots themselves only get cleaned when they’re broken–so this can be once every few years.

“Rule number one: never consume any liquid that is not in a can or bottle,” Kamalani warns. “Those water tanks are never cleaned, and they are disgusting.” It is common wisdom among airline personnel that any water coming straight from the faucet is likely laden with bacteria–and a 2019 study conducted by Hunter College corroborates Kamalani’s intel. 

Researchers analyzed the drinking water aboard planes on 11 major American airline carriers and 12 regional airlines. Each was ranked on a scale of 5 being the best and zero being the worst, with scores above 3 indicating a relatively clean water supply. However, results found that 7 major airlines scored under a 3. 

A low score would be indicative of the presence of microorganisms in the water, including the total coliform bacteria. This is significant according to researchers because their presence in drinking water can indicate disease-causing pathogens as well. According to the report, major airlines scored as follows: 

  • Alaska: 3.3
  • Allegiant Air: 3.3 
  • Hawaiian Airlines: 3.1 
  • Frontier: 2.6 
  • Southwest: 2.4
  • Delta: 1.6
  • American Airlines: 1.5
  • United: 1.2
  • JetBlue: 1
  • Spirit: 1

“Talk to any flight attendant,” Kamalani warns, “we rarely, rarely drink the tea or coffee on board.”

Some extra reading for the high achievers: 

How these British flyers learned about the Queen’s death. 

Is United leaving JFK airport this October? 

Grandma and Grandpa fly for free? On this airline, yes.