A flight attendant has told Business Insider an insider tip that will make you view the drinks trolley in a whole new light.
"Flight attendants will not drink hot water on the plane. They will not drink plain coffee, and they will not drink plain tea," they said.
And that's because not even the cabin crew know the cleaning schedule for the tanks where the water is kept.
In fact, tests in 2013 found a high percentage of airplanes had bacteria in the water served on board.
So next time you spot a member of cabin crew purchasing a cup of coffee before boarding a flight, you know why. And you might want to do the same.