A metallic taste, a blue-green ring in the sink drain, or a green stain on a white tub often points the same way: the water is pulling metal out of the pipes and fixtures instead of leaving them alone. This is corrosive water, and it is a different problem from hard water. Hard water leaves crusty white deposits. Corrosive water leaves color, taste, and sometimes leaks.
What you can notice yourself
Start with what you can see and taste. Look for blue-green or greenish stains around faucet bases, at the drain under the sink, and in the bottom of a toilet bowl or shower pan where water sits. Notice whether the taste is metallic or sour, especially first thing in the morning or after water has sat in the pipes for hours. Check whether the hot tap tastes worse than the cold one. Hot water tends to speed up metal loss, so a hot-only problem is worth writing down.
Small leaks at copper joints or pinholes in copper pipe can also come from corrosive water, although many other causes produce leaks too. Keep a short written list of stains, taste notes, and leak repairs, with the room and when you noticed each one. A list you keep yourself is more useful to a tester than memory.
Check whether it shows up at every tap
Run each tap for a few minutes, then taste water from the first draw after the line has sat overnight. If the taste and staining appear at only one fixture, look at that fixture and its supply line first. If they appear at every tap and keep returning after you clean them, the water supply is the more likely source. Also note whether any plumbing has been replaced, because new metal and mixed metals can change how the water behaves.
Get a lab test, not a guess
A stain tells you something is wrong, not what. The useful step is a water sample sent to a laboratory certified for drinking water testing. It can measure pH, copper, zinc, and lead, along with other metals. Ask the lab for its sampling instructions. Labs often want a first-draw sample taken after the water has sat unused for several hours, and sometimes a second sample after the tap has run. Follow their directions exactly, and keep the paperwork that comes with the bottles.
Do not rely on a home test strip for this decision. Strips give a rough sense of pH, but they cannot tell you the copper or lead level, and those are the numbers that matter for your pipes and for what your household drinks. If anyone in the home is pregnant or caring for a baby, mention that to the lab and to your doctor, since lead results carry more weight for them.
Ask who is testing and what they will fix
Before you hire anyone, read what the quote actually covers. A provider who offers to treat corrosive water should explain whether they plan to adjust pH, use a neutralizing media, or recommend a different approach, and what lab results should show before and after. Ask whether they will retest after installation and who pays for that retest. Use the 2026 Directory of Water Treatment Providers in Missouri to shortlist providers, and read how providers are reviewed before you rely on any listing.
What to bring to the first call
Bring the lab results, your stain and taste notes, a list of the fixtures affected, and whatever you know about the age and material of your pipes. Those four things let a provider tell you whether the fix is a treatment unit, a pipe repair, or both. Without them, any number a provider gives you is a rough estimate at best.