I came across this video recently, it shows a product to use to get rid of water spots. Might be worth a go. I‘m going to get some myself to try.
https://m.youtube.com/watch?v=sjtN9AzvuJM&feature=youtu.be
Here is a link to the product itself:
ChrisRs and the other pro detainers on here may be able to add some more info about it