Was just about to recommend this...definitely works amazing.

 

I was looking through my Griots Garage catalog today and saw they have a water softener. Its for people with hard water (kind leaving water spots). This is an in-line filter from your outside faucet to your hose. Check it out... kinda spendy but I'd get one if I still lived at my parents where I was always fighting water spots.

http://www.griotsgarage.com/catalog....1001&SKU=37244