How does it hold up with hard water?

The Nebia by Moen Quattro shower stands up well to hard water. That said, if you have very hard water, over time build up can occur just as any household fixture will. However, the solution is quite simple. Just clean using white vinegar, by tying a bag filled with the solution around the head or the wand, and let it sit for 20 to 30 minutes. Any build-up will completely dissolve.