Tom might know what they do in the PNW.
I know what some say they do
I was on a tour once at a brewery nearby, and the tour guide told me that they distill all of their brewing water.
They surely filter it to remove the chlorine, but there's no way they distill it. Not even RO, with the water we have (very soft water with low overall mineral content).
I've never taken a formal survey or anything but from random conversations over beers I can say that, like homebrewers, their procedures seem to vary. Some are much more rigorous about mineral additions, others are not. A lot depends on the personality of the brewer and when/where they got their training, not to mention the recipe they're brewing.
I'll be at the Washington Brewer's Guild meeting in a few weeks, if I remember I'll ask a bit more in depth and see what people are doing.