Water that has been left to sit in glass can leave rings of discoloration and a residue of what is called “scale.” This happened to me recently, both on a crystal champagne glass that I didn’t want to abandon (it looked ruined with the scale), and a glass cooking bowl that had been used outside for a project. I had a senior moment, forgot what I know about how to clean this problem, and scrubbed and scrubbed to no avail (you realize why the residue is called scale!), and even sent them through the hot dishwasher, thinking for sure that heavy duty detergent and heat would work, but no such luck.
When I remembered what to use for scale, it of course worked immediately and like magic! This trick can be used anywhere hard water minerals build up, such as in the shower.
Vinegar performs the magic! All you need to do is pour straight household vinegar into the bowl or glass with scale and it instantly dissolves the minerals and it is crystal clear clean. For the shower stall or around a sink faucet, soak a washcloth in straight vinegar and lay the cloth over the area for as long as needed.
Heinz white distilled vinegar is made of vegetables, not petroleum.
For glass you can use organic apple cider vinegar, but this can stain fabrics, so use with care.