Its a pet peeve of mine, culprits include LCY & SEN. Totally agree about mixed taps although it takes a while for the water to heat up and you can add a purification tablet (although you are not likely to carry them on a business trip).
No frills carriers try and charge you for water (and try getting served in turbulence).
That said I saw a bottle filling up station in LHR T4. They should be everywhere. Could you include it in an airport operating licence? (OK unlikely.)