I've been tormented by this stupid hard water stain at the base of my ice machine/water door in my fridge. I have tried every product...including my go to/never fail Mr. Clean sponges (I get nothing for saying that, I promise, I just really like them). The hard water stain remained.
THEN someone suggested vinegar. I poured some vinegar into each slot. I let it sit for about ten minutes. I ran a sponge through each slot when I was done letting it sit, and the water lifted right off. I can't even explain how much therapy this just saved me. OK, maybe not that far, but....it really bothered me b/c I cleaned and cleaned. Good ol' vinegar...I need to buy it in bulk!