Blue-green stains around a sink drain, under a faucet, or along the bottom of a tub are a common sight in Arnold homes, and they can look alarming. The stain is usually a sign that metal is leaving a pipe or fixture and settling on a surface. Before you scrub or buy anything, it helps to figure out where the color is coming from, because the answer changes what you do next.
What Causes the Color
Copper is the usual source. Copper pipe, brass fittings, and some faucet parts contain copper, and when water is slightly acidic or otherwise corrosive, it can dissolve small amounts of that metal. As the water evaporates or sits, the copper compounds dry as a blue or green film. Staining often shows up where water pools, such as around drains, under the rim of a sink, or in a tub that dries slowly.
Other colors point elsewhere. Reddish-brown stains usually suggest iron, and black or dark brown specks often come from manganese. Both are more common in private well water. Hard water typically leaves white or gray crusty scale instead of a blue-green film, so a colored stain is a reason to look past hardness alone.
Look for the Pattern
Notice which taps carry the stain. If it appears mostly at the hot tap, the water heater and hot side of the plumbing may be involved, since heat can speed up corrosion. If both hot and cold show it, the source may be the supply side or a fixture part. Note whether the stain returns quickly after cleaning, or whether it appears only after water has stood overnight. Write these details down, since they will help you or anyone who checks your system later.
Simple Checks You Can Make
- Run the cold tap for a few minutes before using water for drinking or cooking, especially after the house has been unused for a while.
- Think about any cleaner you used recently. Some products contain copper or are strongly acidic, and residue can leave colored marks.
- Wipe a stain with a mild cleaner and see whether it returns within a day or two.
- Look at the drain stopper, faucet base, and any exposed brass parts for green crust, which points to a fixture-level source.
- If you have a water softener or treatment system, note whether the stain started after a change in settings or equipment.
When to Test
A home test can give you a starting point. Simple pH test strips show whether the water leans acidic, and many labs can measure copper in a water sample. When you choose a lab, ask whether they test copper in a first-draw sample from the tap you care about, and whether they can report pH, hardness, and metals together. Lab results are easier to use when you describe the stain pattern you saw.
Public water reports describe Arnold tap water as hard, which tends to show up as scale rather than blue-green film. A stain that is unusual for your area is worth a closer look, not a guess.
If You Have a Private Well
Well owners in Arnold should be aware that the EPA is actively addressing lead and heavy metals in private wells tied to the SW Jefferson County Mining Superfund area. If your property is in the south or west part of the area and you see colored stains along with a metallic taste, include lead in your sampling plan. Ask the lab for lead testing specifically, since it is not always part of a standard panel. A stain alone does not show whether lead is present, and only a lab sample can answer that question.
What to Do Next
- Map where the stain appears and which taps carry it.
- Run the cold tap and note whether the color changes.
- Test pH, and request a copper test from a lab if the pattern points to plumbing.
- If you are on a well in the south or west part of the area, add lead to your test list.
- Avoid strong acidic or bleach cleaners on stained fixtures until you know the source.
A clear record of the stain pattern, the test results, and the date of each check gives you something concrete to act on, whether you clean the fixture, adjust the water system, or bring in someone to look at the plumbing.