I think water from taps in the galleys is perfectlty safe to drink. Airlines would face major problems if they made people ill by giving them unsafe water to drink. It may not always taste the nicest though.
At my previous airline, we sold bottled water to PAX, and gave out water from the galley taps to those who didn't want to pay for it. It's the same at home - you either decide to drink the water from your tap, or go to the supermarket and buy bottled water.
Having said that, at my current airline (where we give out drinks, rather than sell them), we pour cups of water from large bottles for PAX, unless we happen to run out of the bottles though...in which case we might revert back to using the galley taps.