The main reasons you should be cautious about drinking airplane coffee are related to the water quality and cleanliness of the coffee-making equipment onboard. Airplane coffee is brewed with water from the plane's water tanks, which are rarely cleaned and often located near or connected to lavatory systems. This can lead to bacterial contamination and unpleasant flavors. Additionally, coffee machines on planes are not frequently cleaned, further increasing the risk of contamination. Flight attendants themselves often avoid drinking coffee made from these water tanks. However, the water used is boiled during coffee preparation, which kills most bacteria. Still, the overall hygiene and the fact that water tanks may harbor bacteria make airplane coffee less safe or appealing compared to bottled beverages. Some aviation mechanics and airline personnel suggest the risk is low due to regular cleaning practices, but many travelers prefer to avoid it as a precaution. In summary, it is generally advised not to drink airplane coffee because the water tanks may be dirty, the machines rarely cleaned, and there is a potential for bacterial contamination despite boiling. For safer options, the recommendation is to choose bottled or canned drinks instead.