Hard water stains

I am not sure if you would be willing to try what we do in our home. When we feel more apt, we clean our sink with "zonrox", the disinfectant multi-purpose cleaner (oh well I forgot how it is technically called, because that's the name we call it here in the Philippines). But when the dirt is really something that sticks, well, try using muriatic acid... I mean, worse case scenario right? Be careful though. It's highly corrosive. It should not touch your skin, nor should you inhale it's smoking odor. Wear gloves and mask. It would help you scrape off those nasty 'ect'. But again, the process would be a little nasty. And it should be done with much care, and with no children horsing around.

Baking soda, try baking soda on the stains and rub. Sometimes a little vinegar like a small amount of vinegar to a larger amount of baking soda helps, too. But some of these new sinks scratch just by looking at them so test a part that isn't easily seen by people before you got wild cleaning it. You'll have to clean it this way often for it to stay easy. Take care and let me know how it works out. Also dishes, white dishes. Now I'm talking rust colored staind, you didn't way what kind of hard water. Calcium and / or sulfer are different. Take care