Black or brown staining and a bitter metallic taste point to manganese. It has two thresholds that get conflated: staining starts around 0.05 mg/L, but the health advisory level is 0.3 mg/L — six times higher. Knowing which one your result is near decides whether this is a laundry problem or a health one.
Two numbers, six times apart
Manganese is the contaminant where the aesthetic and health thresholds are far
enough apart that conflating them changes the decision.
Threshold
Value
What it means
EPA Secondary Maximum Contaminant Level
0.05 mg/L
Black to brown colour, black staining, bitter metallic taste
Health Advisory level (Penn State Extension)
0.3 mg/L
The health-based reference point
EPA states it “does not enforce” Secondary Maximum Contaminant Levels — they
exist “for aesthetic considerations.”
So a result sitting between the two — above the staining guideline but well
under the health advisory — means your laundry has a problem and you do not.
Most manganese results land in exactly that gap.
That distinction matters because manganese results are frequently quoted at
homeowners as though any exceedance were a health finding. Ask which number is
being referenced.
Telling it apart from iron
They travel together and are treated together, but they stain differently:
Stain colour
Metal
Orange, rust, reddish
Iron
Black, dark brown
Manganese
Both also come in two forms, and the form decides the equipment. Draw a glass
and let it stand:
Clear at first, then particles form — dissolved. Can pass through a
softener at low concentrations.
Particles visible immediately — already oxidised. “Oxidized forms of iron
and manganese will foul the softener resin.”
That is the same glass test used for iron, and it gives
the same answer for both metals at once.
Treatment
Because iron and manganese are treated as a pair, Penn State Extension’s bands
are given for the two combined:
Combined iron and manganese
Approach
3–10 mg/L
Manganese greensand filter
Above 10 mg/L
Oxidation followed by filtration — chlorine, potassium permanganate or hydrogen peroxide
Below those ranges, low levels of dissolved manganese can be handled by a
softener, with the same caveats that apply to iron: pH above 6.7, and nothing
oxidised reaching the resin.
Manganese greensand is named for exactly this job. The media oxidises
manganese and iron on contact and filters out the resulting particles, which is
why it appears at the middle of the range rather than at either extreme.
Black staining points to manganese, orange to iron, and the two are treated as a pair because they travel together. Keep manganese's two numbers apart: 0.05 mg/L is where staining starts and 0.3 mg/L is the health advisory, six times higher, and most results land between them. That gap means a laundry problem, not a health one. Use the same glass test as for iron to establish the form, because oxidised manganese fouls softener resin exactly as oxidised iron does. Step up to greensand or full oxidation as the combined figure rises.
Who this is not for
Black staining is not always manganese. It can also come from a failing water heater anode, from sulfur bacteria, or from black mould in fixtures rather than in the water. A test distinguishes them; a photograph does not. This page also does not cover manganese in surface water systems, which behaves differently.
Questions
What causes black stains in sinks from well water?
Usually manganese. EPA lists "black to brown color; black staining; bitter metallic taste" as the noticeable effects above its Secondary Maximum Contaminant Level of 0.05 mg/L. Iron stains orange or rust coloured; manganese stains black or dark brown. The colour distinguishes them before a test does.
What manganese level is safe in drinking water?
Two numbers do two different jobs. EPA's 0.05 mg/L is an aesthetic guideline it does not enforce — exceeding it means staining and taste. Penn State Extension cites a Health Advisory level of 0.3 mg/L, six times higher. A result between the two stains laundry while remaining under the health advisory, and most results land in that gap.
Does a water softener remove manganese?
Only dissolved manganese, and only at low levels. Penn State Extension warns that "oxidized forms of iron and manganese will foul the softener resin." If your manganese is already oxidised — visible as particles the moment you draw water — it must be removed before the softener, not by it.
Sources — 8 claims
EPA — Secondary Drinking Water Standards: Guidance for Nuisance Chemicals EPA's Secondary Maximum Contaminant Level for manganese is 0.05 mg/L, above which the noticeable effects are black to brown color; black staining; bitter metallic taste. (captured 2026-09-09) Limits: An SMCL is a non-enforceable aesthetic guideline, not a health limit. EPA states it does not enforce these levels. Never present exceeding an SMCL as a health risk.
