Does anyone know whether the tap and/or shower water in the rooms is potable/drinkable? Or is it softened?

Softened. But contact the hotel and inquire about that for a more accurate answer

It certainly is not salt water...

It's drinkable and filtered. They use a water softener system to make it enjoyable when showering or bathing. Comfortable place to stay. The Odds are definitely going the houses way. They don't publish too much on winner's, sadly enough.

Salt water

That's a really good question. I don't know personally but I think I will find out.