Manganese in well water

Best for

Homes with black staining or a result above 0.05 mg/L, pH of 6.5 or higher, and manganese up to about 1 mg/L.

Wrong fit

Homes with a bottle-fed baby and manganese above 0.1 mg/L should switch the baby's water now, before choosing a filter. Wells above 1 mg/L need chemical oxidation.

Tradeoff

Manganese is harder to oxidize than iron, so filters that handle iron easily can let manganese slip through. Always retest the treated water.

What manganese looks like

Manganese occurs naturally in rock and soil, and groundwater picks it up the same way it picks up iron. The two often show up together. The difference you see is color:

• Black or dark brown stains in toilets, sinks, tubs and laundry.
• Black specks or a dark film that settles in a glass or in the toilet tank.
• A bitter, metallic taste.
• Stained laundry and scaling on plumbing, which Minnesota also lists.
• Water that looks clear at the tap and darkens after standing, because dissolved manganese oxidizes slowly in air.

Manganese stains at much lower levels than iron. The EPA’s secondary guideline is 0.05 mg/L (ppm) for manganese, compared with 0.3 mg/L for iron. That is why a well can have black stains with an iron result that looks fine.

Is manganese a health risk?

Unlike iron, yes, at higher levels. Your body needs a small amount of manganese, and most people get enough from food. Minnesota puts the recommended intake for children over eight and adults at 1,900 to 2,600 µg a day, and says infants should get 600 µg or less a day. The concern is long-term drinking water exposure. The Minnesota Department of Health says children and adults who drink water with high manganese for a long time may have problems with memory, attention and motor skills, and infants may develop learning and behavior problems. Minnesota also notes that the body absorbs manganese from water more easily than from food. Bathing and showering are not the concern: Minnesota says drinking water above its guidance can be harmful, but bathing or showering in it is not.

The EPA’s drinking water health advisory sets a lifetime level of 0.3 mg/L to protect against possible neurological effects. For short exposures of one to ten days it gives 1 mg/L, but it advises using 0.3 mg/L even for short exposures in infants younger than six months.

None of these numbers are enforceable for private wells. They are the best guide you have for deciding when manganese moves from a cleaning problem to a health problem.

How to test

Manganese is not always on a basic well panel, so ask for it by name. Minnesota suggests testing for manganese especially if an infant drinks your tap water. Levels vary widely, even within one region. In a Minnesota Department of Health study, groundwater in southeastern Minnesota tended to be below 50 µg/L, while southwestern Minnesota tended to be higher, with some wells above 1,000 µg/L, and other parts of the state showed no clear pattern. A neighbor’s result is not a reliable stand-in for your own test. Minnesota also suggests checking whether your county has a program that makes testing easier.

Use a state-certified lab and ask for:

• Manganese
• Iron, since the two travel together and filters are sized on the combined total
• pH, because manganese needs higher pH to oxidize
• Hardness, if you are considering a softener
• Total coliform bacteria and nitrate, the basic safety tests

Labs may report manganese in mg/L or in µg/L. 0.05 mg/L is the same as 50 µg/L, and 0.3 mg/L is 300 µg/L. The guide to testing your well covers sampling, and the test results tool builds a treatment plan from your numbers.

What level needs treatment

Minnesota’s guidance says 100 µg/L or less is safe for an infant who drinks tap water or formula made with it, and 300 µg/L or less for an infant who never drinks tap water or formula made with it, and for everyone over one year old.

Treatment options

Manganese is harder to remove than iron. Penn State Extension notes that it needs higher pH to oxidize, that birm filters need pH of at least 7.5 for manganese removal, and that chlorine is not recommended for very high manganese because it requires a very high pH to work fully.

For most wells with manganese under 1 mg/L, iron under 7 mg/L and pH above 6.5, a single air-injection filter covers both metals. SpringWell’s whole house well water filter is one option built to those limits. If your manganese is higher, or the filter lets manganese through, a chemical injection system ahead of a filter is the next step. For a baby’s water, an under-sink reverse osmosis system is a sensible second barrier even with whole-house treatment.

Order of treatment

1. Sediment filter, if there is sand or grit.
2. pH correction if pH is below 6.5. Manganese oxidation works poorly in acidic water; see acidic well water.
3. Iron and manganese filter.
4. Softener, after the filter.
5. UV, if needed, last.

If you have both iron and manganese, size the filter on both. The iron in well water page covers the iron side.

Maintenance and retesting

• Retest the treated water after installation and again after a few months. Manganese can pass through a filter that is removing iron well, and black stains coming back are an early sign.
• Backwash and regeneration. Oxidation filters need a drain line. Greensand needs permanganate regeneration on schedule.
• Clean fixtures once. After treatment starts, remove old black deposits so you can see whether new staining appears.
• Test before a baby arrives. If a pregnancy or a new baby is coming, test manganese even if you tested years ago.

When to call a pro or the health department

• Manganese above 0.3 mg/L in a home with infants, children or a pregnant woman.
• Manganese above 1 mg/L, or combined iron and manganese above 10 mg/L.
• Black staining that continues after treatment.

Work with a licensed water treatment professional for system design. For health questions about your results, call your state health department. State pages for well owners are listed under states.