I don't know of an entire book devoted to water in brewing, but several brewing books have chapters on water and minerals. It depends on what level of insight you are looking for, but here are several I have and use:
Palmer's "How to Brew" book and website does a good job on a basic level.
Fix's "Principles of Brewing" has a chapter with a very basic description of the chemistry for non-chemists.
Daniels' "Designing Great Beers" has a chapter with a little more depth than the other two, but not much.
I had a quick look at my brewing text, Briggs and Hough, "Malting and Brewing Science" and didn't see much about water in specific that would be more useful than the above books.
If you are looking to buy a book I would recommend Palmer or Daniels as being the most useful. Palmer is more basic and how to, Daniels is more in depth and focused on styles and designing recipes. Both are great books.