I had some hard water spots on my windows from the previous owner of my truck. I tried everything I could think of and nothing would take them off. Well, I was on the LS1 board the other week and someone posted about the same problem. There were people suggesting the same stuff I've already tried, but one person suggested "Bar Keeper's Friend." I just bought some earlier tonight and gave it a shot. Well, with a little scrubbing (ok, a lot of scrubbing) all the water spots came off. I was amazed how well this stuff worked. So, if any of you have hard water spots on your truck, buy some "Bar Keeper's Friend." I highly recommend it.