I love it when people search instead of asking new questions. So much knowledge is buried here on BYC but a simple search brings it to the surface and a new comment lik this from NewtonZ gives it more exposure. But the answer is still the same, a bit of rust on galvanized steel just makes some micro nutrients/minerals more available. Far less danger from a bit of zinc or iron in the water than the chemicals leaching out of plastic. The only reason to paint the rust spots is just to make the waterer last longer. A good red primer will have lots of iron oxide, a zinc chromate primer is a bit less safe as chromate is a strong oxidizer, dangerous to the lungs as a powder, somewhat an irritant and not great for ingesting. But, the chromate part of zinc chromate is an etching substance, as it etches the iron to prepare the iron/steel surface for bonding with the primer it kind of bonds/dissolves with the iron and becomes less bio available and more safe. Plus the zinc will cover up what little remaining chromate is left in a bio available state. Just research the ingredients in the coating you want to patch the rust spots with and your chickens will be fine. And just remember the scientific solution for pollution is dilution, even with radiation and heavy metals, mixing it with water makes it far more safe than a bird eating the stuff. Good luck, stay away from the plastic please!
