An orange or brown ring forms at the surface of the water in my toilet bowl. What causes that?
Some small amount of the dissolved iron from the water mains is carried into the bowl where it eventually meets oxygen at the surface and is oxidized. In the oxidized form iron can no longer stay dissolved in the water, and plates out on the porcelain surface. Iron oxide can stick to most any surface. It isn’t unusual for water that carries a very small amount of iron (0.1 parts per million) to, over a long period of time, cause bathtub surfaces and shower curtains to show an orange tint. The iron will not be visible in the water, but after it hits the air and the iron oxidizes, the iron oxide begins to accumulate on the surface. Most bathroom cleaners will remove this iron oxide.
