Steps:
- Richard explains a green-stained shower is likely caused by soft water.
- Richard says when the pH level of the water drops below 6.5, the water becomes acidic. That means elements like iron, manganese, lead and sodium could be in the water.
- When the water becomes acidic, it can start to eat away at the copper pipes.
- To illustrate how acidity works, Richard places a copper pipe into a vinegar and sodium solution for 45 minutes. Then lets it sit for another 45 minutes. That quickly you can see a buildup of patina from oxidation.
- That greenish/blue oxidation can build up over time. When water flows through the pipes, it picks up that corrosion and comes out of the showerhead and into the shower itself.
- Richard explains to combat soft water, homeowners could get a calcite acid neutralizer tank. That uses white marble limestone to dissolve into the water and neutralize those extra elements and bring up the pH level of the water.
Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, explains that acidic soft water can actually eat away at your copper pipes from the inside: “The water’s coming out of the shower head, it’s taking water. It’s eating little parts of the copper pipes on the inside coming off and bouncing off him and then going back on the shower.” Those green stains you see are dissolved copper being deposited on your fixtures — a sign your plumbing is actively corroding.
Pro Tip: Richard Trethewey recommends getting your water professionally tested to determine the right treatment: “You should go out and get your water tested… certified state lab or a good outfit that knows what they’re doing with water.” Once you know exactly what’s in your water, you can install a whole-house filter with the right media inside — whether that’s sediment, activated carbon, or limestone for highly acidic water.
Soft water damage isn’t just cosmetic — it can compromise your plumbing system over time. As Richard Trethewey notes in This Old House Magazine, water that is acidic or corrosive can wear away copper pipe from the inside, especially when combined with turbulence from burrs left during installation or excessive water pressure from undersized pipes. If you’re seeing green stains on fixtures, it’s worth inspecting exposed copper pipes and fittings for signs of pinhole leaks or pitting.
