+1 to FlyGuy. I've never heard of it affecting "hoppiness", just mash efficiency. It's more a lack of certain minerals that can affect perceived hop bitterness in certain styles of beer. But that can be corrected by adding minerals to the boil. If your water is low in minerals, for example, and you're brewing a stout, you'd want to add gypsum, etc. to the boil. Low mineral water can be good though because that usually means the pH is relatively low too, which can be good for the mash.
The main thing to do is to find out what your water pH is (typically). If it is "normal" (upper 6's - low 7's), you'd want to either do an acid rest or use 5.2 pH buffer. Personally, I lucked out. My well water pH is ~5.7, so the mash can lower its pH pretty easily to the low 5's. So, I never correct mash pH and get high 80s to low 90s brewhouse efficiency.