What is that dark brown or black film in my toilet bowl?

Black bowl Brown Dark Film toilet

What is that dark brown or black film in my toilet bowl?


The Association has been asked this question often over the years. It is not uncommon for a dark brown or black film to appear at the toilet bowl water line and below. This brown or black film is generally by Iron and Manganese mineral deposits that naturally occur in our water source. Fortunately, it is easily removed.

Geoffrey Mac


Here is a clip from the municipal water authorities in upstate Buffalo NY.


Why is there a black ring inside my toilet bowl?

This has nothing to do with water being delivered to your household. This is mildew caused by

room temperature, facility usage and lighting. We suggest a chlorine-based bowl cleaner, and

more ventilation during showers.


My situation is as follows;


This was the case in my home, the extractor vent for the bathroom was ineffective. You may have closed windows, poor ventilation etc. In my case, a little investigation found that this extractor vent fan, vented into the attic an not out to the atmosphere (poor construction). As a result we stop turning on this extractor fan to prevent mold and mildew buildup in the attic. So, during showers and toilet use we got this mildew build up from moisture in the toilet. See, there is a REASON for these ventilation systems in homes with windowless bathrooms. (town-homes, apartments, houses etc).


Improve you ventilation and you will eliminate this problem.

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