They do not used bottled (or boxed) water for coffee.
That comes from the coffee machine built into the galley, which uses the aircraft’s onboard potable water tanks.
Those tanks are filled from a hose by the ground crew during refueling.
(At least for major US airlines. I understand some other carriers serve instant coffee packets. Even then, the hot water still comes from the aircraft tanks.)
I wonder how air Canada reconciles this. There was a popular globe and mail article a while ago that gave awful rankings to air Canada's water tanks -- so the company put up signs in the bathroom saying the water is non-potable and called it a day.
Not super comforting if they're then using the same 'non-potable' water to make coffee...
Is there any reason to expect there would be "toxins", given that it's just water? I can imagine how there might be accumulated toxins it's a pack of chicken breasts left in a hot car for 8 hours, but if it's water it should be fine? After all, boiling water is a tried and true way of making water safe to drink.
Yes, there are substances that slip through, but it works well enough for most cases that it's probably fine. Otherwise you get into weird edge cases like "what if there are prions in the water?!?" or whatever.
Heavy metals are a big problem, especially from cheap brass fittings common in outdoor water hoses.
Indoor plumbing, by contrast, uses copper and/or plex tubing and so there’s near zero risk of metal poisoning (caveat on cheap plex fittings- don’t do that.)
That comes from the coffee machine built into the galley, which uses the aircraft’s onboard potable water tanks.
Those tanks are filled from a hose by the ground crew during refueling.
(At least for major US airlines. I understand some other carriers serve instant coffee packets. Even then, the hot water still comes from the aircraft tanks.)