Iron and manganese in well water: stains, taste and what fixes them

The problem: stains, specks and a metallic taste

The EPA lists the signs. Iron above 0.3 mg/L can cause rusty color, sediment, a metallic taste and reddish or orange staining. Manganese above 0.05 mg/L can cause black or brown color, black staining and a bitter metallic taste.^[source] Some homes get both, so laundry turns dingy while fixtures pick up orange streaks and black rings.

Water from these wells often comes out of the tap clear, then turns cloudy or colored after it sits. Dissolved iron and manganese are invisible until air reacts with them and they turn into solid particles. That's why a glass that looks fine at first can stain a sink over weeks.

Likely causes

• The rock itself. Groundwater with little dissolved oxygen can release iron and manganese from minerals in the aquifer.^[source] The state's Union County assessment notes that elevated iron and manganese turn up statewide in many rock types.^[source]
• Acidic water. Low-pH water can corrode iron and steel parts in the well and plumbing. If your water is also acidic, see our page on low pH and acidic well water. That problem usually has to be fixed first.
• Iron bacteria. Some wells grow iron bacteria, which can show up as reddish-brown slime in toilet tanks and fixtures.^[source] That calls for well disinfection, not just a filter.

How common is it here?

Very common. In wells tested through North Carolina's state lab from October 1998 to May 2019,^[source] these shares were above the thresholds UNC's county tables use:

These are wells whose owners chose to test, not a random sample, so treat them as a sign of how common the problem is, not a prediction for your well. County details are on the Union, Cabarrus and Lincoln county pages.

Two different thresholds, and why that matters

You'll see very different numbers for "too much" iron and manganese, depending on the source. The difference is about what each number measures:

• EPA secondary standards: 0.3 mg/L iron, 0.05 mg/L manganese. These are non-enforceable guidelines for cosmetic and aesthetic effects like staining, color and taste.^[source] In micrograms, that's 300 µg/L iron and 50 µg/L manganese. Above these levels is where staining and taste problems start.
• Health-advisory levels: 2,500 µg/L iron, 300 µg/L manganese. UNC's county well tables use these higher numbers. The tables label the iron figure an NC DEQ health-advisory level and the manganese figure an EPA health advisory, and they note that separate, lower aesthetic standards exist.^[source] USGS also uses 300 µg/L as its health-based screening benchmark for manganese.^[source]

How testing works

Iron and manganese are both on North Carolina's required panel for new wells,^[source] so if your well is newer, start with that report. Our guide to reading your new-well test results walks through it. For any well, we use a certified-lab panel through our well water testing service that covers:

• Iron and manganese, reported separately, because they're treated differently.
• pH, because it determines which treatment works and whether the water needs neutralizing first.
• Hardness, since it affects equipment choice and whether a softener belongs later in the system.
• Arsenic, because some local wells with iron problems also carry arsenic, and iron-oxidizing pretreatment is part of some arsenic systems.^[source]

Treatment categories

The basic idea is the same for every option: turn dissolved iron and manganese into solid particles, then filter them out. The EPA lists aeration, coagulation and filtration as removal methods for these metals.^[source] For homes, the common categories are:

• Oxidizing media filters. A tank of media coated with manganese dioxide oxidizes and traps iron and manganese, then backwashes on a schedule. NC DHHS lists iron-oxidation and manganese-dioxide filters as pretreatment options for wells.^[source]
• Air injection or aeration plus filtration. Air oxidizes the iron ahead of a filter tank. No chemical feed is needed, but there's more equipment to maintain.
• Chemical oxidation plus filtration. A small feed of chlorine or another oxidizer handles higher levels, and it also helps when iron bacteria are present.
• pH correction first. Low pH can interfere with some oxidation methods, so a neutralizer often comes ahead of the iron filter.

Which one fits depends on your iron and manganese levels, pH, flow rate and whether bacteria are involved. We size equipment to your lab numbers, not to a brochure. If hardness is also high, a water softener may come after the filter, but only if your hardness test shows you need one.

When to bring in a pro

If you see red-brown slime, if stains come back soon after cleaning, or if a filter you already own has stopped keeping up, get a full lab panel before buying anything else. Whole-house iron filters connect to your main water line and need a drain for backwash. Here's how installation works.

Iron filters need periodic backwash checks and media replacement over time. A Care Plan bundles that with an annual retest.