Why there are black specks in your well water, and how to fix it
Black specks that smear into a black powder between your fingers are usually manganese. Hard grains that settle fast are sand or silt. Manganese stains at 0.05 mg/L. The EPA's lifetime health advisory is 0.3 mg/L, and Minnesota's guide for babies is 0.1 mg/L, so test it, especially if a baby drinks the water.
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Step 1: Rub a speck between your fingers
The Wisconsin DNR suggests this test. Catch a few specks on a white paper towel and rub them.
- They smear into a black powder. That's manganese, often with some iron.
- They feel hard and gritty and don't smear. That's sand or silt from the well. See our page on sand in well water.
Other manganese signs: dark stains on laundry (Wisconsin DNR), black or brownish-black stains in toilets, tubs, and sinks (Minnesota Department of Health), and standing water in a tub or toilet tank that looks gray or black (Penn State Extension).
Step 2: Check for a rotten egg smell
Penn State lists black, greasy stains as a sign of hydrogen sulfide. If your black stains come with a rotten egg smell, start with our rotten egg smell page.
High manganese can affect your health
Manganese dissolves out of bedrock into well water, per Penn State. The EPA's secondary guideline is 0.05 mg/L (milligrams per liter), the level where black stains and a bitter metallic taste show up.
There's also a health side. The EPA set a lifetime health advisory of 0.3 mg/L, and says babies under 6 months shouldn't go above it even for a short time. The Minnesota Department of Health uses a tighter number for babies under 1 year: 0.1 mg/L (100 micrograms per liter) or less if the baby drinks the water or formula made with it. Minnesota says children and adults who drink high-manganese water for a long time may have problems with memory, attention, and motor skills.
Our manganese page has more on the health side.
Step 3: Test for manganese and iron
Ask the lab for manganese, iron, pH, and hardness. Both Wisconsin and Penn State say treatment choice depends on how much of each you have.
Your state or local health department may test for free. Once you have results, our test results tool explains each number.
Pick the fix that fits your levels
| What the test shows | Options from Penn State and Virginia Tech |
|---|---|
| Low manganese and iron, combined under 5 mg/L | Water softener, if the manufacturer recommends it for manganese. Penn State says softeners work best when pH is above 6.7. Minnesota found softeners lowered manganese in a Dakota County study. |
| Higher levels, about 3 to 10 mg/L iron and manganese combined | Oxidizing filter, such as manganese greensand. pH adjustment may be needed. |
| Over 10 mg/L combined | Chlorination followed by filtration. Penn State says chlorine isn't a good fit for very high manganese, so ask about other oxidizers. |
| Drinking water only, at one tap | Reverse osmosis at the kitchen sink |
If a baby drinks the water and your manganese is over Minnesota's 0.1 mg/L guide, use water that's under that level for the baby's drinking water and formula until treatment is in place and a retest shows it's working.
When to call a pro
Call a water treatment professional once you have test results, especially if you have both iron and manganese, or manganese with low pH. Wisconsin says the device has to be able to remove the amount of iron and manganese in your water, and Penn State says the levels decide which options are practical.
Questions people ask
Are black specks in well water dangerous?
The specks themselves are mostly a nuisance. The concern is the manganese level. Above the EPA's advisory of 0.3 mg/L, or above 0.1 mg/L for infants per Minnesota, it's a health issue worth treating.
Why is my toilet tank black inside?
Penn State says standing water in a toilet tank can look gray or black when manganese is present.
Will boiling remove manganese?
None of our sources list boiling as a treatment for manganese. Minnesota warns that boiling can raise the level of some contaminants, such as nitrate and arsenic. Use a softener, an oxidizing filter, or reverse osmosis instead.
Where this comes from
- Wisconsin DNR, My Water Has Black Particles
- Wisconsin DNR, My Water Stains Fixtures Black
- Penn State Extension, Common Drinking Water Problems and Solutions
- Penn State Extension, Iron and Manganese in Private Water Systems
- Minnesota Department of Health, Manganese in Drinking Water
- Virginia Cooperative Extension, Household Water Treatment
- Minnesota Department of Health, Bacterial Safety of Well Water
- EPA, Secondary Drinking Water Standards
- EPA, Drinking Water Health Advisory for Manganese