Chip,
That is always a problem when you have minerals in your water at relatively high concentrations. Most common are calcium, manganese, and magnesium but of course iron will be present as well as a few others.
As already posted, the best you can do is get a filtration system for your water supply that could be rather costly. There are lots of types and I'm not an expert.
Or, get some good materials for buffing. You may want to get a water hardness test kit and find out if you need to be softening it. Basically this is an ion exchange process where you trade sodium for other ions which you don't want.
Alternatively you could purchase deionized water for washing your car, typically less than $1 per gallon at stores and use this for the final rinse. However, this doesn't always do the trick.
That is about the best I can do at the moment. I do remember a product that was offered at one time to pre-treat your water in the bucket before use, I'll see if I can find it. However, I doubt it would be that effective as I'd imagine it would try to drop the minerals (calcium, iron, etc.) out of solution as a precipitate into the bottom of the bucket. Might be worth something though.
R
[ September 09, 2002: Message edited by: Ron Earp ]