[doublevanosrc]

My car is black and has hard water spots on the flat surfaces(hood, roof, trunklid). I hit up the hood yesterday with Meguiars M105 and then followed with M205 while applying some pressure using an orbital buffer and it looks awesome now(almost new). I would say it removed all the water spots and like 98% of swirl marks and light scratches. If it's really severe you can do wet sanding, I did it once with a kit from 3M and it does work wonders. I would recommend trying some compounds from Meguiars and see how far they get you.