Don't drink the tap water in Hong Kong without boiling it first
Get $50 for writing a tip!
The water being distributed is very safe for drinking, but a lot of the older buildings have old and corroded piping in place. If you're staying at a decent hotel or in a newish condo, chances are the water is fine, but the problem is you never know and there's always a good chance that the piping is bad in the your building
For what it's worth, locals here never drink the tap water directly without first either boiling it or filtering it. In fact, most locals I know drink bottled water most of the time
For brushing your teeth and stuff it's perfectly fine and no one I know has any issues with it so don't worry about that