“They will not drink plain coffee, and they will not drink plain tea.”
Posting on US knowledge-sharing site Quora, another former flight attendant wrote: “The water on the plane is absolutely disgusting, the tanker which the water comes from is literally never cleaned.”
This means that the tap water passengers are drinking could be full of bacteria.
Previous testing on planes found the tap water to be unsanitary with some planes testing positive for the presence of microorganisms in the water, including bacteria.
source: express.co.uk