Water Marks on Glass

[Challo]

I bought a E46 convertible earlier this year and it was a bit neglected by its owner and unsure if she actually ever cleaned it. It seems all the side windows, and particular the rear glass screen have severe hard water marks.

I tried to give it a clean with a household window cleaner but think I need something more abrasive.

Anything anyone can recommend that wont damage the glass?

[Challo]

Thanks all. Will try those options