Water problems library
Black stains
Dark deposits in toilet tanks, on fixtures, or in laundry.
Possible causes
- Manganese is one possible cause — common in groundwater.
- Mold or mildew around (not in) fixtures is another.
What evidence helps
A lab test covering manganese; visual checks distinguish fixture mildew from water-borne deposits.
Honest next steps
Don't assume manganese
It's possible, not proven, until tested.
Test the water
A well panel that includes manganese and iron answers this directly.
Then choose treatment
Confirmed manganese responds to specific oxidizing media — matched to the measured level.
Black stains have several causes. We won't name yours without a test.