If you often order a coffee on a flight, then you might want to look away now.
A flight attendant has revealed that the water used for coffee can contain dangerous E.coli bacteria, reports the Daily Mail.
"Betty", who says she works for a major American airline, told Vice that the water used for coffee is the same as the water used for the plane toilets.
The attendant, who wished to remain anonymous to avoid losing her job, warned passengers: "Don't drink the coffee on airplanes."
Responding to a question about the grossest thing on airplanes after the bathrooms, she told Vice: "It's the same potable [safe to drink] water that goes through the bathroom system.
"We recently had a test for E. coli in our water and it didn't pass, and then maintenance came on and hit a couple buttons and it passed.
"So, avoid any hot water or tea. Bottled and ice is fine, of course."
The revelations were part of a broader discussion about what it's really like to work in the air.
EasyJet confirmed to FEMAIL Food & Drink that water stored on an aircraft is used for making hot drinks and for flushing the toilet.
However a spokesman added: "There is absolutely no chance of any cross contamination due to the system's plumbing design.
"This is common place amongst most aircraft manufacturers and airlines. Fresh water is loaded onto the aircraft daily."
"Betty" is not the first to advise against drinking coffee on a flight.
The Environmental Protection Agency (EPA) discovered in 2012 that when they tested water on commercial airlines, 12 per cent of tested positive for coliform bacteria, which points to other bacteria such as E. coli being present also.
Travel + Leisure magazine also spoke to a flight attendant for American Airlines, who said the water tanks in planes "are probably only cleaned out every six months to a year".
In 2016, an AskReddit thread revealed some alarming anecdotes from professed airline employees.
"The coffee is absolutely disgusting because the no one washes the container that goes out every morning," said one. "The station agents who get paid way too little don't give a s*** about cleaning it. I certainly didn't when I worked for [redacted].
"Also, because we weren't given the proper supplies to clean it. We pretty much just rinsed it out and dumped coffee into it," the person added.
There's another reason why coffee and tea on a flight never tastes as good as on the ground.
The low cabin pressure means that water will boil at 90C rather than 100C, which can result in a poor-tasting brew as teabags are not usually designed for cooler water.