Keeping water marks off of shower glass doors...

Use CLR bath and kitchen. It works great.

you can buy glass cleaners at any auto parts stores for water spots.

We definitely want to stay away from any cleaning products that have an abrasive. Your local grocery or department store will have products specifically for cleaning soap scum. Some products will work better than others depending on the type of mineral content in your water. The best product is one where you don't have to do an excessive amount of scrubbing to remove the hard water and soap scum stains. Be sure to follow the manufacturers instructions for the best results. Again depending on the mineral content of your water you may have to try a few different products until you find one that works the way you want it to. There are also products you can purchase that you would spray onto the glass after a shower to prohibit the buildup of soap scum.

I would try baking soda and vinegar mix. Just sprinkle the soda in the sink and add the vinegar a bit at a time. Let it sit for awhile,use a soft scrubber,rinse,and wipe with a soft,dry,cloth.
You could also try CLR. Just follow the directions on the package.

Norwex Descaler is the absolute best thing I've found for hard water build up on any surface, including glass shower doors and shower/sink fixtures. When I moved into my current house last year, the bathtub and shower head were disgusting! They were white with years of built-up hard water residue. Repeated application of CLR and a ton of elbow grease just couldn't get it off. When I tried Norwex DeScaler for the first time, it removed ALL of the soap scum and lime in the FIRST application.

This stuff is enzyme based - free of hazardous chemicals and enviro friendly. The enzymes in the DeScaler actually eat the soap scum! I just spray it on, wait 5 -10 minutes, and wipe off with my wet microfiber cloth (also from Norwex). It's incredible. It works better and faster than CLR, or any other chemical alternative I've tried. It's fume-free and can be used by people with chemical and environmental allergies.

You can buy it from a Norwex Rep, or order it online - a good site is www.Norwex-Healthy-Cleaning.com. Hope this helps.