Black Slime On Faucets – What It Is And How To Get Rid Of It

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Have you ever noticed dark-brown or black slime on faucets, spouts, aerators, shower heads, in toilet bowls or other bathroom fixtures? Harmless manganese bacteria causes it, and in this post, I will tell you how to get rid of the black gunk. I will also list methods that do not, or only temporarily, work.

Mentioned Brands & Products

APEC RO-90 – Reverse Osmosis Drinking Water System


MOLDetect® One Sample Mold Test Kit


Hach 146700 Manganese Test Kit


Water quality in Atlanta

What causes black slime and gunk on bathroom fixtures and in toilet bowls?
Black slime on our bathroom faucet aerator

I was born and raised in Salzburg (Austria), which is not only known for Sound of Music and Mozart but also for excellent water quality. Ok, maybe the last part isn’t commonly known unless you are from there.

In Alpharetta, Georgia, water smells and tastes different. The first thing I noticed when moving here was the chlorine taste in tap water. I keep joking with fellow Europeans, who live in the US, to bring a small bottle of chlorine on trips back to Europe so we can make the water there taste like what we got used to here in the US.

Besides taste, I have noticed another nuisance with our drinking water. Black slime or gunk was building up around bathroom fixtures. On faucets, this nasty stuff seems to accumulate around spouts and aerators and form black flakes or slime. In toilet bowls, you may notice it as dark stains.

What is causing black slime in faucet aerators?

I found myself removing that black gunk on faucets and spouts a lot lately, so I searched the Internet for answers. Unfortunately, there isn’t a lot of factual information available. Unless you already know what it is, so you can use the proper search terms. Keywords like “pink shower mold” often lead to ridiculous answers, such as “call the health department” or “sue your landlord.” So I decided to dig a bit deeper and soon discovered oxidized manganese and harmless bacteria feeding off of it to be the cause of this black slime.

Interestingly enough, the problem doesn’t occur on every faucet or appliance, but it could manifest as:

  • A black shower head or faucet
  • Pink or black stains in toilet bowls
Black slime on faucets? Learn what it is and how to get rid of it!
Black gunk/slime on aerator

Manganese, as well as iron bacteria in water, can stain drinking water, fixtures or even laundry. Most drinking water has traces of dissolved iron and manganese. When these minerals come into contact with oxygen (from water or air), they oxidize. Iron can tint water (and things it comes in contact with, such as fixtures) red and manganese can tint water black.

Manganese is a naturally occurring metal that can be found in different types of rocks, soils, and sediments; and typically occurs in lakes, rivers, and underground water supplies.

The black slime that accumulates on spouts is bacteria that feed on oxidized iron and manganese in the water.

Manganese: A naturally occurring mineral
Manganese: A naturally occurring mineral

Is Manganese (bacteria) harmful?

Neither manganese nor the bacteria are considered dangerous and a risk to your health in levels as they occur in our drinking water. The WHO recommends maintaining a concentration of 0.05mg/l in drinking water. Lower levels can be easily achieved by filtration.

Manganese and iron in drinking water

Depending on the concentration of manganese in your drinking water you have different options. Unfortunately, Fulton County doesn’t spell out manganese levels in its annual Water Quality Report. That is because there are no federal drinking water standards for manganese. So if you want to know how much manganese is in your drinking water, you have to get it tested.

I called our water provider, the Fulton County Water & Sewer Billing and Collection Division. The gentleman on the phone told me that the problem of black slime in water pipes could be resolved by flushing the main line.

Our house was built in 1989, and if the main line was never flushed, I could imagine that mineral deposits, including manganese, built up over the years.

He came out the same day flushed the main line and told me that the problem should be fixed. Unfortunately, flushing the main line did not resolve the problem; we still have the black slime and gunk. I called the county, and someone from the water department came out to run some tests. All ad-hoc tests confirmed that the water quality was within the county guidelines, but the gentleman admitted that he had never seen this issues before. That statement made me wary because I was surely not