Most homeowners who search for water treatment are answering a taste or a stain. Some of those problems come from minerals in the supply. Others come from the water attacking the pipes it flows through. Copper corrosion is one of the second kind, and it looks different from the problems that are usually blamed on the water source. Learning to tell them apart keeps you from buying equipment that cannot fix the cause.
What copper corrosion looks like in your house
The signs show up in specific places, so start with a walk-through rather than a guess.
Look for blue-green or teal staining in the sink basin around the drain, on the faucet base, and under the aerator at the tip of the faucet. Check the shower floor and the tub at the drain. Staining that appears where water sits, or where it splashes and dries, is a strong pattern. Stains that are sharply blue-green, rather than orange or brown, lean toward copper rather than iron.
Next, look at the taste and the water itself. A sour or metallic taste is the most common complaint. It is often strongest first thing in the morning, after water has sat in the pipes overnight, and it may fade after the tap has run for a while. Some people notice that the cold tap tastes different from the hot tap. Compare them side by side. A difference that follows the hot line can point to the water heater or hot-side piping, which is worth mentioning when you describe the problem to anyone who comes out to look.
Finally, check the age and material of the plumbing. Ask whether the home has copper supply lines, when the plumbing was last replaced or repaired, and whether any section was changed in a way that mixed metals. Mixed metals at a joint can speed corrosion. Your home inspection report, the seller's disclosure, or the plumbing permit history may answer some of these questions.
What to test before you compare equipment
Stains and taste alone do not confirm copper corrosion. A water test does. Ask for a lab test that reports the water's pH and the level of copper, and ask whether the sample was drawn from a cold tap that had been sitting unused, since that sample shows what the pipes are releasing. A sample taken after a long run may look fine and miss the problem entirely.
Compare the reports you get, and be cautious about any single number from a single test. Water chemistry can change with the season and with how long the water has sat. If you have more than one result, look at whether they agree.
Also ask who reads the results and what they recommend. A treatment company that tests your water should explain what the numbers mean for your pipes, not just which product it sells. Ask it to say in plain words whether the problem is in the water or in the plumbing, and what evidence supports that answer.
Questions to ask before you buy anything
Treatment for corrosive water is different from a filter or softener, and the wrong choice can leave the pipes losing metal. Before you agree to any equipment, ask these:
Does the proposal address corrosion, or does it only address taste at the faucet? A filter at one tap does nothing for the water already moving through the rest of the house.
If the water is found to be corrosive, what adjustment is proposed, and how is it monitored over time? Ask how the system is checked after installation and who receives the follow-up results.
Will the company test the water again after the change, and will it give you the results in writing? A written before-and-after comparison is the clearest way to see whether anything changed.
What happens if the pipes are already pinholed or the stains are spreading? Ask whether the company will say so plainly and refer you to a licensed plumber, rather than promising that treatment will repair the damage.
When to stop and call a plumber
Water treatment does not repair pipes. If you see a drip at a joint, damp spots on a wall or ceiling, a sudden drop in pressure, or stains that keep growing, call a licensed plumber before anything else. A plumber can locate a leak, judge whether a section needs replacing, and tell you whether the corrosion has gone far enough that treatment alone will not be enough.
If anyone in the household has questions about drinking the water, a doctor or the local health department can advise on what to do while you sort out the source. Keep a note of what you see and when, and bring it to every visit.
When you are ready to look for a company to test and assess the water, the 2026 award winners for greater St. Louis page is a place to start your list. Check each company's test process and its written findings before you choose one.