Why does my water leave blue-green stains?
Blue-green stains on sinks and fixtures are a telltale sign of copper dissolving from your pipes — usually because the water is acidic (low pH).
The likely causes
Low-pH (acidic) water slowly corrodes copper plumbing. The dissolved copper leaves blue-green stains where water evaporates, and can give a metallic taste.
Is it dangerous?
The stains themselves are cosmetic, but they signal that copper — and potentially lead, from solder in older homes — is leaching from your pipes. Copper is a health concern at high levels, so blue-green staining is worth confirming with a test.
How to tell what it is
A pH test showing acidic water plus a copper test confirms it. Staining that is worse where water sits (a dripping faucet, the tub) is a strong clue.
The fix
Treating the root cause — raising the pH with a whole-house neutralizer — stops the corrosion and protects your pipes. At the drinking tap, a reverse-osmosis or under-sink filter certified for copper removes it from your water.
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