Ask a flight attendant what they won't touch in the cabin and the answer, surprisingly often, is the tea and coffee. The reason comes down to where that hot water comes from: not a bottle, but the aircraft's onboard tanks — the same system feeding galley taps and, on some widebodies, the lavatory water dispensers.
There's real evidence behind the squeamishness. The US Environmental Protection Agency has found that roughly one in eight aircraft failed water safety standards in its surveys; a 2004 sample of 158 planes turned up coliform bacteria on 13% of them, with two aircraft testing positive for E. coli. A more recent study of over 35,000 samples across 21 airlines found about 2.7% positive for coliform, with E. coli detected 32 times. Delta and Frontier came out on top for water quality; American and JetBlue scored poorly. Mechanics push back, though, describing regular tank flushes with diluted bleach and frequent swaps of the coffee machines themselves.
What about boiling? Cabin pressurisation lowers the boiling point to roughly 195°F at a 7,000-foot equivalent — but the WHO says bacteria die at around 170°F, so by that logic your in-flight tea should be fine. A US flight attendant of 35 years told reporters crews drank 'gallons of coffee' on international crossings without problems. Yet others who've seen inside the tanks during maintenance stops say they stick to sealed drinks, and one even brewed her own coffee in the galley oven using bottled water.
A few other onboard quirks are worth knowing. Diet Coke pours far slower than other sodas at altitude — cabin pressurisation and artificial sweeteners make it extra fizzy, which drags out the bar service. The ice is fine, though: it comes from the catering company, not the aircraft tanks. And cold drinks in the main cabin are actually mixed with bottled water anyway; tank water only feeds the coffee and tea makers, the galley taps and the lavatory dispensers.
If you want to play it safe, the consensus is simple: buy a large bottle of water at the airport, or bring an empty one and fill it at a fountain — aim for about 8 ounces of water per hour in the air. Cabin pressure and dry air dull your taste buds too, which is why tomato juice is genuinely the most flavourful choice at 30,000 feet, as a Lufthansa study found. And go easy on the alcohol: lower cabin pressure makes each drink feel closer to two on the ground.
Bottom line: the water is probably safe — tested, regulated and drunk daily by pilots and crew — but plenty of the people serving it choose bottled. If the smell of chlorine in your coffee puts you off, there's your answer.
