And how do I get rid of it?
Here are some theories of what this red line is caused by. The last one is the correct one, but I include the first two because they are examples of wrongness, and we are all about that on the Internet, aren’t we?
The first explanation, historically, is that the red substance found in damp places, which today include the inside of your toilet or other places in your bathroom or kitchen, but in those days (before porcelain toilets) included other human-made as well as natural locations, is that this is the blood of Christ. This wass especially thought to be true when this red substances was found on bread, and especially when the bread was the Eucharist, the piece of bread that Catholics believe is the actual body of Jesus Christ, which you then eat. Blood coming out of anything linked to Christ, especially the actual body of Christ in the form of a wafer of bread, is about as intense as it gets if you are a Medieval Christian.
The second explanation, the one I see all the time today, is that there is something wrong with the water supply. We often see the red film or line forming in toilet bowls, or behind the fixture on your sink, or in showers or tubs, blamed on the poor quality of the city water supply, and often, this theory links the red substance to iron in the water causing rust.
The red substance of which we speak here is not rust, and it is not blood of any kind. It is Prodigiosin, a red pigment. When you see this red pigment, you are actually looking at a very likely thriving and living colony of the bacterium Serratia marcescens.
Serratia marcescens can be a human pathogen. It is responsible for a percent or two of the known hospital based bacterial infections that have become such a problem. It affects children more than adults, can cause urinary tract infections, and sometimes it exists as strains that are resistant to bacteria.
The military in the US and UK used Serratia marcescens as a “harmless” bacterium in germ warfare trials, between 1950 and 1980. This made sense because it was thought to not cause disease, but being red, was easy to find and spot in a culture to test the efficacy of germ warfare delivery devices. Serratia marcescens was, therefore, spread across the San Francisco Bay region once, and a large area of England. In the case of San Francisco, it may have caused a spike in certain illnesses, and may have killed at least one person. In any event, it turns out it is not harmless.
Serratia marcescens is not the blood of Christ, and it is also not from your water supply. It is fairly ubiquitous so it can come from the air, from your body, from wherever. It probably does NOT come from your water supply because living Serratia marcescens would be killed in routine water treatment.
So do get rid of it. Most people don’t need to worry. It is not that pathogenic. But children may be somewhat susceptible, and anyone immune compromised is at risk. Experts concerned with infectious disease don’t have this in their toilets at home.
Do not scrub the Serratia marcescens from your porcelain devices using a metal scrubber. That will ruin the porcelain finish and create crevices and scratches at the microscopic level. Bacterial such as Serratia marcescens love those crevices and scratches.
Do not put bleach in the back of your toilet system. That will ruin metal and rubber parts and cause leaks.
Do use a bleach based cleaner in the toilet bowl, on the sink in the shower, etc. to clean away this red stuff.
Clean it up where you see it, and do a general cleaning of the entire kitchen and bathroom — all of your kitchens and bathrooms and places this stuff is seen in your house — at about the same time. Maybe you’ll get all of it, or most of it, and it won’t come back or it will take a long time to reappear. If you clean a red spot here or there in your bathroom but not all of the at once, it will migrate back to where you removed it more quickly. If you wipe away the line around your toilet bowl but ignore the underside of the rim (that yucky area you can’t see without doing a Kavanaugh) it will come back.
But really, it is going to come back no matter what, eventually. Perhaps you should frequently use a brush without cleaning fluid, and occasionally a bleach-based substance on a brush, to clean these areas on a more regular basis than you are doing now. Chances are you see the red rim around your toilet water in the bathroom you hardly use, and do not see it in the toilet in the bathroom you usually use and thus clean regularly. What you should be doing is cleaning unused toilets in your house on a regular basis (weekly, bi-monthly, whatever) instead of ignoring them.
There is, of course, rust in some water, and that may be what you’ve got. But rust is not pink and does not form that line around the edge quite the same way. Medieval Catholics knew about rust, and thought this red stuff was blood. They just don’t look the same.
Serratia marcescens will, of course, coat the entire surface of the underwater part of your toilet but it tends to concentrate around the edge due to evaporation. It is also left behind when tiny puddles form, say, in the built-in soap dish in your shower or behind suction cups that are meant to hold stuff up in the shower, or behind the fixtures on your bathroom sink, etc.
I personally use one of these (though you might prefer this style) in the bathroom, and yes, I admit, I use this to clean both parts of the shower (down on the floor) and the bathroom (changing brushes, of course).