Yep, I'm sure. First of all Iron should not be a problem if you run on city or piped water. Wells are another story as they do not receive treatment, so I completely agree with you.
Now let's talk a smidge about hard water. Hard water is simply water with "heavy metal ions". Metal will not readily dissolve in water so you actually have metal ions. Sodium and Potassium have a weak positive charge and do not form strong ionic bonds. Therefore they disassociate from their negatively charged anions easily.
For example:
Take Na (sodium) and Cl (Chloride). Na has a charge of +1 and Cl has a charge of -1 thus they are attracted. When attracted they form a salt NaCl which is sodium chloride or "table salt". Now then when water is introduced they rapidly dissolve. Calcium and Magnesium have a charge of +2. When they form salts, they have a much stronger bond to the anion (negatively charged atom). Thus they do not dissolve as rapidly when water is introduced. In plain English heavy metal ions like Calcium and Magnesium are twice as attracted and bond twice as strong. Whew!
Thus as water evaporates off your car, if high Calcium water is left behind it will form salts that are VERY difficult to dissolve and get into the pores of your clear making them hard to physically remove too. Thus waterspots. If you exchange Calcium for Sodium, what a water softener does, you will leave behind Sodium water spots (though often sodium evaporates away with the water leaving fewer and smaller spots that are MUCH easier to dissolve with water). A softener is not a substitute for proper technique. What it will do is be more forgiving. So you wash your car (by the way soap is an anion and is attracted to Calcium and Magnesium and will stick to your car as well!) and rinse as you go. You finish washing and the first parts are dried because you washed in direct sunlight with spots. You go back and re-rinse the roof (dissolving the spots) and then chamois it (waffle weave MF towels are great!) then do the windows and pillars and dry, the hood and dry, the trunk and dry, the sides and dry. You do not spray the water, you let it pour out of the end of the hose so you don't wet your previous work. No water spots.
Now the spot free rinse is accomplished with DI water but good god it's so expensive! Just use good technique and cheap water. For a few more minutes of your time you could greatly decrease overhead and increase profits! My experience with pay and sprays is this. They recycle water so they are not DI and they still leave spots, again in my personal experience.
