[Tagging] Feature Proposal - RFC - Water tap

[Bryce Nesbitt]

There are a number of possible shades of potable:

* It's not designated, but in an area where all faucet water is
potable (e.g. major cities, fountains in rome).
* It's designated potable.
* It's designated as untested (e.g. "drink at your own risk")
* It's designated non-potable by color or specific signage.

The tagging should definitely incorporate the physical color or sign
associated with the tap.
The tag encoding some invisible or informal knowledge I am not sure belongs.