I've never developed the taste for coffee -- on the ground or in the air not have I tried drinking from an aircraft tap -- but if it concerns you it may make you rest a little easier to know that for US flagged aircraft the EPA regulates aircraft water systems similarly to more traditional (i.e. municipal) water systems: https://www.epa.gov/dwreginfo/aircra...ing-water-rule
it may not make you feel better to know that I first learned about this a couple years ago when I stumbled across an the EPA citation to an airline (can't remember if it was UA) for violating the rules.