The one beverage to avoid on planes
When flying, it might be better to steer clear of ordering coffee or tea according to a recent study published in the journal PLOS One. The water used for brewing these beverages on planes comes from the aircraft's water tanks, which aren’t cleaned as frequently as they should be, and potentially harbor harmful bacteria. Beyond sanitary concerns, coffee is also a less-than-ideal choice on planes due to its dehydrating effects. For safer hydration choices while airborne, passengers are better off sticking with bottled water or other pre-packaged drinks.
Source
Handschuh, H., Ryan, M. P., O'Dwyer, J., & Adley, C. C. (2017). Assessment of the Bacterial Diversity of Aircraft Water: Identification of the Frequent Fliers. PloS one, 12(1), e0170567. https://doi.org/10.1371/journal.pone.0170567
Additional Reading
https://dailypassport.com/one-drink-never-order-airplane/
https://www.travelandleisure.com/drinks-you-should-never-order-on-flight-nutritionist-7508081
https://www.foodandwine.com/is-airplane-tap-water-safe-8658075