Have you ever wondered why you don't see flight attendants enjoy a hot cup of coffee or tea? It's not because they're on duty, and it's not because they're not allowed to -- as it turns out, there's a very particular reason why, and you're probably not going to like it.
The water used in hot drinks on flights is tap water from the aircraft water tanks. In this study, the EPA (Environmental Protection Agency) tested this water onboard 158 randomly selected passenger airplanes. While 87.4% met the EPA's standards, 12.6% did not.
20 of the randomly selected aircraft's water supply carried total coliform bacteria. Just in case you're not familiar with what that is, in layman's terms it's poop bacteria. As if that wasn't enough, two of the aircraft also tested positive for E.coli.
Even after retesting 11 aircraft, 8 of these still did not meet the EPA's quality standards. Maybe you're better off playing it safe and going for a can of coke or bottled water on your flights from now on.