I found a crusty white powder forming on my water shutoff valves under the sink. Should I be worried?

To determine if the white powder is simply harmless mineral buildup, consider the location and extent of the deposits. Mineral buildup often appears uniformly around plumbing fixtures and is usually dry and flaky. If you can easily wipe it away with a damp cloth, it’s likely just surface-level mineral residue.

Another indicator is the absence of any signs of moisture or leaks. If the area surrounding the valves is dry and free from water stains or discoloration, this suggests that the buildup is not associated with a leak. You can also perform a simple test by applying a few drops of vinegar to the powder. If it fizzes and dissolves, it’s a good indication that the substance is calcium carbonate.