If You See Green Residue in Your Sink, This Is What It Means

What is causing that blue-green stain in the bottom of your sink? Algae? Toothpaste? Nope, the culprit is copper!

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Did you know that the Statue of Liberty and that green stain in your sink have something in common? They’re both the result of a chemical reaction. While it’s nothing of immediate concern, it’s important to understand what it is and where it’s coming from.

What Is That Green Stain In Sinks?

That green stain in your sink is actually copper deposited from pipes or fixtures. You’ve likely seen it pool around your drain, but the issue isn’t with your sink or drain. It begins inside the pipes before you even turn on the water.

What Causes That Green Stain In Sinks?

That blue-green stain is caused by the effect of corrosion or a slow disintegration within the home’s plumbing. Here are a few reasons why pipes corrode:

Stagnant water

If copper water pipes have water sitting inside them for long periods, the inside of the pipes can start to corrode.

Water pressure

If the water pressure is too high, the sheer velocity of the water can cause wear and tear over time, leading to corrosion. Maximum pressure in a home should not exceed 80 psi (pound-force per square inch).

Water pH

If the water has an unusually low pH (low alkalinity; less than 6.5) or an unusually high pH (greater than 8.5), pipes are more likely to corrode. Master plumber Bret Hepola of All City Plumbing in Minnetrista, Minnesota says, “Water pH is the primary culprit of the blue-green sink stain.”

Installation error

If air is getting into the pipes, or the connection from fittings joining the pipes have not been properly installed, it can cause corrosion in the pipes. Over time, these imperfect scenarios make the copper in your pipes break down.

When you turn on the water, these small deposits from the pipes run out through your faucet and into your sink. And while it can tint the water green, it’s not always visible to the naked eye.

However, it is noticeable when it forms a blue-green ring in the sink. That coloring results from a chemical reaction between the copper deposits caused by corrosion and oxygen, forming copper hydroxide carbonate. Oxidation is why the Statue of Liberty, which is made of copper, has turned green over time.

How To Remove That Green Stain In Sinks

Michael Dean, a water expert and co-founder of Pool Research, suggests mixing vinegar and baking soda. “Create a paste, [then] apply it to the stained area and wait at least 10 minutes before wiping/scrubbing it off,” he says.

If the stain is too stubborn, Dean suggests trying a stronger acid than vinegar. However, he says, stronger chemicals may damage the surface of the sink.

Some other common solutions include:

  • Salt;

  • Dish detergent;

  • Lemon juice;

  • Cream of tartar;

  • Ammonia;

  • Toilet cleaners containing sodium bisulfate.

How To Stop the Corrosion That Causes Green Stain in Sinks

While these solutions leave your sink clean and stain-free, they won’t fix the root cause. Another green stain will likely form in the sink over time. And eventually, if left untreated, this corrosion can cause failures in the plumbing pipes. Depending on the cause, there are a few steps you can take to prevent further corrosion:

Test the water

Checking your water’s pH level is a good place to start. A plumber can test your water for you, but there are plenty of DIY options, including at-home tests. If you want to test for more than pH, complete water testing kits can also detect lead, bacteria, iron, fluoride and copper.

If you find that your pH level is off, an acid-neutralizing filter can be installed. “The correction of pH is often approached by the installation of an acid-neutralizing filter,” Dean says. “However, there are pros and cons to these systems, and depending on the pH level of your water it may or may not be worthwhile going in this direction.”

Patch The pipe

If you find pinhole leaks in your pipes or suspect one may be forming, the easiest and quickest fix is a piece of rubber from a garden hose or similar and a couple of hose clamps. Other options include:

These repairs are only temporary fixes until a pro makes a proper pipe repair. A pro will also diagnose and offer solutions to fix the cause of the leaks.

Mackenzie Edwards
In addition to her work with Family Handyman, Mackenzie is a contributing commerce writer for Bustle Digital Group's lifestyle sites. She also owns and operates a copywriting studio in Nashville, TN. Mackenzie is an avid DIYer, sharing her budget-friendly home improvement hacks with her growing social media and blog audience.