In 2015, a study in the International Journal of Environmental Research and Public Health found that there was more bacteria in the trucks delivering the water than in the original water source. If you're thinking none of this matters because heating the water will kill off any disease, think again.

It is generally advised to avoid drinking hot water—and by extension, coffee or tea—on a plane because the water used to make these beverages comes directly from the aircraft's onboard storage tanks. According to a major 2026 airline water safety study, these tanks are difficult to clean and can harbor various types of bacteria, including coliform and even E. coli in rare cases. While the water is heated to make coffee or tea, it rarely reaches a full boil (which is required to kill most pathogens), meaning any bacteria present in the tank can still be active. Furthermore, the pipes and hoses used to fill these tanks at different airports worldwide are not always subject to the same rigorous sanitation standards. Flight attendants themselves often avoid the "hot water" beverages for this very reason, preferring sealed bottled water or canned sodas. For your own safety and peace of mind, it is best to stick to drinks that come from a sealed container rather than those prepared using the plane's internal plumbing system.