Two more comments...First, if you are not using the 2.0 version of the EZ water calc do yourself a favor and download the newer version. It's much improved.
Second, if you really want to learn more and get more accurate results, download Martin's (mabrungard) spreadsheet at Bru'n Water
He's put a lot of effort into this and it's really good. Even better is that on his website and in the spreadsheet itself is a ton if information about water for brewing, as well as detailed instructions.