[ChevLoRay]

Before I retired (against my will), I worked for Alcoa, where we created chemicals from alumina. The by-products inevitably ended up on windshields as well as the rest of the vehicle. It was an alkaline-based product, so it would leave spots on everything.

So, I decided to put some Rain-X on my windshield one day and it was only after many failures that I finally hit on what worked for me.

First, clean the windshield with any good window cleaner. Then, go over the entire surface with some 0000 steel wool (4-aught). Then, go over the windshield with window cleaner, again. Then, the steel wool. After that, you good to go to put some Rain-X on it. Hopefully, after you get the Rain-X on the glass, you won't see any more water spots, regardless of the chemistry of the water (hard, soft, whatever).

I've had well water that was sweet and pure. Just a couple hundred feet away was some of the foulest well water you could ask to avoid.....plenty of sulphur and iron, so stink it did. I didn't wash my car with it. But, calcium is an alkaline, so maybe some CLR used sparingly, will help you get rid of the spots. Good luck.