I used vinegar (as a home remedy) and it worked but only minimally.

Then i went to a car shop (like Concorde) to buy ELEVO WATER MARK REMOVER. It cost me just around 250bucks. I used it on my civic's windshield, 4 windows and rear window and my mom's pajero windows too.

Tanggal lahat ng water mark stains! It's definitely worth it coz even after using it on both cars, more 2/3 pa ang laman ng bottle. Cheaper and less hassle than taking it to a detailing shop indeed!

Plus it's very easy to use. No hard rubbing required. Just spread it lightly with the sponge that comes in the box! I used gloves because it could sting or itch the skin.. Instructions on the box advises you not to use it on mirrors. Only clear glass windows.