I've been using a 3-gallon galvanized waterer for 2 years, and very recently, it developed some nasty rust spots on the floor of the inside, as well as around the edges of both the base and the cap thingie. If I don't scrub it out and refill it at least once a day, the water they're drinking is a little rusty. I imagine this is not good. (I do change their water daily, but when I'm on away, I'm not positive my husband or petsitter is so diligent.) I've got very hard well water, which explains the normal sediment I see (like inside my SS tea kettle). But rust? Nobody at my local Agway has ever seen this. I searched old posts here, and now I'm wondering if it may have been caused by my adding a little apple cider vinegar to the water for a week or two awhile back, on my vet's orders. The weird thing is, I'd given them a little vinegar in the past, though not for such a long period of time, and never saw any rust. Maybe the prolonged exposure corroded it? I broke down and bought a new waterer yesterday, but for that price, I would love to be able to use the old one as a secondary station - but not if it's unhealthy! Can I safely use Rustoleum or something to paint over those spots inside?