Have you tried vinegar? Spray and rub it on with newspaper. it goes on cleaner than with paper towels (and is free). Vinegar can clean almost anything.
I had the same issue with my new truck. The sprinkler wet the car down and the results were horrible. I used CLR on the glass and it seemed to work well. But its pretty nasty stuff so you need to be careful when you use it.
Check out this web link it has some interesting facts about cleaners.
The last thing. Most properly installed softened water systems bypass the outside hose in order to prevent the softener having to be recharged to often. As usually all the hose does is wash car and water lawn. Check to see if this is the case in your home. That may explain why you have these stains.
Try cascade or any of the dishwasher solutions. Use spray bottle to apply.