There's some white stuff on my filter—what is it?

White residue is mineral buildup. It is harmless and, in the case of the black filters, is no reason to replace them. If it is visible on the black filter, rinse it off under running water and wipe it down. If it is visible on the containers or the spout, scrub it off with a mixture of equal parts water and vinegar. You can also soak the spout in this mixture.