can see the water marks... can't see the paint

here is my suggestions if you can't get yourself an in-line water filter to combat hard water
1. make sure you use a clean wash mitt with the 2 bucket method
2. try washing a panel at a time working from the roof down, dry the panel just after you wash it.. it IS possible to wash panels without getting other panels wet
3. use a drying towel followed up with a microfibre
4. clay, polish and then a few coats of wax will get rid of the marks and lessen the amount of water that sits on the paintwork and increase run off