How to Clean the Black Ring Under the Toilet Rim with 3 simple methods

Does it seem you’re constantly cleaning the black waterline, only to have it come back a few days later? While it may be unsightly and frustrating, it’s actually more common than you think.

So, sit back, relax, and let us walk you through our guide on how to clean the back ring under the toilet rim. We’ll also tell you some of the leading causes and how to prevent them from ever happening again.

Let’s get started.

cleaning toilet rim

How to Clean the Black Ring Under the Toilet Rim

Before we get into the details of removing black waterlines, let’s talk about what causes these murky dark lines in the first place.


There are three primary reasons why your toilet has a black ring around its rim. Take a look.

Bacteria Build-Up

When bacteria build up in the toilet bowl, it can cause a dark pink waterline that turns black if left for a long time.

The main type of bacteria behind this dark line is called Serratia Marcescens. Actually, this pathogen is found practically anywhere there’s humidity and water.

Bear in mind that these bacteria are airborne. So, in the worst cases, it can be highly lethal.

Mineral Deposits

Believe it or not, your water supply could be the culprit behind these pesky black rings.

According to the US Geological Survey, 85% of all homes in the US have hard water. Hard water is the same as normal water, except for its high concentration of minerals.

If this is the case for you, then it’s likely to cause mineral deposits to gather and collect around the rim of the toilet. Then, each time you flush, minerals like magnesium, calcium, and lime accumulate over time, leaving behind that ugly black line.

In addition, these minerals can also clog the tiny holes that allow flush water to stream through. As a result, the bowl can start gathering all types of grime in areas not getting enough water.

Take a close look at the inner rim of the toilet base. Does the waterline appear brown, gray, or copper-like? Then, it’s more likely that the black stain is due to mineral deposits.

Mold Spores and Mildew

Molded toilet

Mold spores are a top cause of the black waterline. Mildew is another primary cause, and it can appear as gray, pink, green, and orange.

Both are typically found in homes in the Pacific region, where the climate is humid, damp, and contains a high moisture content.

If your toilet already gets mineral deposits, it’s quite likely that both mold spores and mildew will start settling on the toilet rim.

Another reason is when waste is left in the bowl for some time without flushing. Humidity and darkness can also trigger the growth of mold and mildew, as mentioned above.

Bear in mind that the risk of respiratory problems increases if there are mold spores being released into the air each time you flush.

They can also cause renal infections and urinary tract infections if not dealt with right away.

Cleaning Methods

Now, it’s time to look at how to finally get rid of that awful black ring.

Method #1: Pour Acids to Get Rid of Bacteria

Acids are the most effective when it comes to removing bacteria build-up. These acids include borax, vinegar, lemons, and hydrogen peroxide.

Start by pouring one cup of acid of your choice. Let it sit for 30–45 minutes. Next, thoroughly scrub the toilet bowl with the brush and flush it.

For stubborn stains, pour one cup of white vinegar and one cup of borax. Then, let it sit overnight before giving the toilet bowl a good scrub.

Method #2: Pour White Vinegar and Baking Soda to Eliminate Mineral Deposits

The easiest and most efficient way to remove mineral deposits caused by hard water is a mixture of white vinegar and baking soda.

First, place half a cup of white vinegar in a plastic container. Then, slowly add 2–3 tablespoons of baking soda. The white powder will neutralize the vinegar and cause it to start foaming up.

This foamy solution makes removing the clingy minerals much more effortless.

Start by pouring the mixture into the toilet bowl. Next, spread the solution with the toilet brush to ensure even coverage.

You can sprinkle another layer of baking soda and let it sit for 15 minutes. Finally, scrub the toilet, then flush.

Repeat once or twice a month to prevent the black waterline from returning.

Method #3: Pour Bleach to Remove Mold Spores and Mildew

cleaning with bleach

Mold and mildew growths need something powerful like bleach to get rid of them for good. It’s one of the best cleaning products and is commonly used to kill a wide variety of harmful pathogens, such as mildew and mold spores.

There are two ways you can go about this. First, you can either spray the bleach onto the rim of the toilet bowl and let it sit for half an hour. Then, scrub and flush for a sparkling finish.

The other option is to pour half a cup of bleach directly into the toilet bowl. You can also add several drops into the tank itself.

Make sure the liquid covers the overflow tube and other parts that make up the flushing system. This way, you can guarantee that all the mold and mildew have been completely wiped out from all parts of the toilet.

It’s worth mentioning that bleach is highly acidic and has a pungent odor. So, make sure you open up the door and window before pouring. Also, gloves are highly recommended to protect your skin against this chemical’s caustic effect.

How to Prevent Black Rings Under the Toilet Rim in the Future

You’ve finally gotten rid of the murky, grungy black waterline, and you’re ecstatic that your toilet bowl is now sparkly white. Yet, you worry that the black line might return and tarnish your bowl once again.

Have no fear. We’ve put together a list of some essential things you should do on a regular basis to keep that dreadful black line away once and for all.

  • Set up a regular cleaning schedule for the entire bathroom.
  • Always flush the toilet before you start to clean it.
  • Consider updating your toilet bowl if it’s old.
  • Use a water softener to treat your hard water supply.


There you have it! Our in-depth guide on how to clean the black rings under the toilet rim.

Knowing the cause for these offensive black lines is only half the battle. The other half is removing them for good.

Luckily, there are several permanent solutions to help you eliminate any unwanted build-up in your toilet bowl. All you need is a few essential items, a toilet brush, and some elbow grease.

Joe Carrow

Reno addict, keen gardener, and baker. I  started blogging in 2012 and have been hooked ever since!

error: Content is protected !!