the only real way around hard water is either a deionization water filter..or a home water softner unit...both are sorta the same....they will remove most of the minerals...calcium...magnesium...these are called carbonates
take your water to your water supplier and have it tested to see how hard it really is..if you have a well..you can get a water test kit from a Aquarium supply store...or home depot...
Yea, quick detailer. It'll help you to get rid of waterspots which formed as a result of the car wash you just did... however, it won't be able to take care of etched in water spots.