Grey Sediment In Toilet Bowl? Here’s The Fix

While toilet bowls aren’t synonymous with cleanliness, we do expect them to at least look clean. Grey sediment in the toilet bowl can make your water closet look anything but. There are ways to get rid of that unsightly stuff, though.

Grey sediment in the toilet bowl is usually caused by scale deposits due to hard water. Bacterial growth or improper cleaning of your toilet are other potential culprits. Scrubbing the toilet bowl with bleach can help you get rid of it in most cases. However, you may have to use muriatic acid to remove stubborn scale deposits. 

How To Get Rid Of Grey Stains In Toilet Bowl

Getting rid of grey stains in the toilet bowl is easier than it seems. You might have to use some elbow grease, but the task requires only a handful of things. 

Things You’ll Need:

  • Angled toilet brush
  • Bleach (or a toilet cleaner containing bleach, such as Clorox or Scrubbing Bubbles)
  • Bucket (optional)
  • Rubber gloves

1. Dry Scrub Your Toilet

Grey sediment in the toilet bowl is generally visible on the bottom, under the water seal. However, the nasty stuff also gathers under the toilet rim.

This is why you should start the cleaning process with a dry scrubbing of the toilet rim – dry scrubbing means cleaning the rim with the dry brush without using any cleaning product.

While you could use any kind of toilet brush you want, an angled toilet brush is your best option. These toilet bowl brushes enable you to apply more force while scrubbing, thanks to the angled handle. Thus, you can remove more deposits in one go. 

2. Clean The Toilet Rim With Bleach

Once you’ve scrubbed under the toilet rim with the dry brush, it’s time to add some bleach. You can use undiluted household bleach (scented or unscented) or a toilet cleaner containing bleach. 

Most people find it easier to use Clorox or Scrubbing Bubbles. These cleaners contain bleach and come in bottles with angled necks that allow for a seamless application of the product under the toilet rim. Squeeze the bottle and make sure the liquid is evenly distributed around the rim. 

Alternatively, pour some bleach into a bucket and distribute it evenly under the rim with the toilet brush. Pour some more product into the toilet bowl and leave it for 15 minutes (close the toilet lid to prevent the bleach vapors from spreading around your home). 

3. Scrub The Toilet 

After about 15 minutes, the bleach has likely killed most germs in your toilet, and you can start scrubbing to get rid of the grey stains. 

Start with the area under the rim and work your way downwards, scrubbing the entire toilet bowl. Scrub the bottom of the bowl vigorously and push the brush as far as it goes under the toilet bend. This should dislodge the grey sediment under the water seal. 

Flush two or three times when you’re done, then inspect the bowl to check if all sediment is gone.

4. Remove Stubborn Sediment

Sometimes, scrubbing the water closet with bleach or toilet cleaner is insufficient. If you haven’t used the toilet in a while, the minerals in the scale deposits may have reached a high concentration, making the sediment difficult to dislodge.

This is where muriatic acid steps in. The acid can dissolve scale deposits and other sediments while also killing germs. However, it can also attack the glazing on the porcelain bowl, so you should only use muriatic acid if other cleaners fail to do the job.

Flush the toilet a few times before pouring in the acid to wash away any traces of cleaners or bleach. Never mix muriatic acid with other chemicals. 

Pour a small quantity of acid into the water in the toilet bowl – you should avoid pouring it directly onto the porcelain. Close the lid and let it sit for 15 to 30 minutes

Put on a respirator and open the lid. Scrub the bottom of the bowl with a plastic toilet brush (the acid doesn’t attack plastics). Flush two or three times when you’re done. 

Warning: Only use muriatic acid in standard toilets with porcelain or ceramic bowls. If you have a Toto toilet or similar, the acid could damage the washlet. 

5. Prevent New Deposits 

Keeping the toilet bowl clean and sanitized is the first step in preventing grey sediment build-up. You can do that by pouring half a cup of bleach into the toilet tank when it’s filling. 

A weekly deep-cleaning and scrubbing are also essential to prevent grey sediment and the build-up of harmful bacteria.

Why Is There Grey Stuff In My Toilet? 3 Reasons

Grey stains in the water closet can easily cause distress when using the toilet. However, they are not always the result of poor hygiene. Here are three reasons why your toilet is stained.

Poor Hygiene Practices

Improper or infrequent cleaning is the main reason why you have grey stains on your toilet. Poor hygiene practices make your toilet a perfect home for various types of bacteria, including sulfur bacteria which causes grey stains

If you also notice orange or hot pink stains, know that they are a sign of Serratia marcescens in the toilet

Bacteria-caused stains are easy to clean with bleach and a brush. If the grey sediment is stubborn, you’re likely dealing with scale or chemical stains.

Unused Toilet 

If you have more than one bathroom in your home, it often happens that you forget to clean the guests’ bathroom if you haven’t had guests in a while. More often than not, the grey sediment in an unused toilet is scale or sediment caused by the impurities in water that had the time to deposit at the bottom of the toilet. 

Flushing Chemicals

You can also cause grey or black stains in the toilet bowl by disposing of chemicals, including hair dye and other hair or skin care products. 

Cleaning a discolored toilet is often harder than cleaning grey sediment caused by scale or bacteria. However, you might be able to remove the stains with bleach. 

Mix equal parts of bleach and water and spread the mixture over the stains with a toilet brush. Leave overnight, then rinse thoroughly in the morning. If the stains are under the waterline, pour undiluted bleach into the water and let it sit overnight. Rinse in the morning and repeat if the stains are not gone.

What Causes Grey Stains In Toilet Bowl?

There are four main causes of grey stains in toilet bowls: hard water, sulfur bacteria, water sediment, and orthophosphates. 

Hard Water

Hard water is the main cause of grey sediments in the toilet. The minerals in the water deposit on the bowl in the form of scale.

At first, the mineral scale is soft and easy to remove with a brush. However, the longer you leave it, the harder it becomes to remove. Sometimes, even muriatic acid can fail to get rid of it if you’ve let it sit for too long. This is why you should scrub your toilet vigorously at least once a week.

Sulfur Bacteria

Sulfur bacteria is generally an indicator of poor hygiene practices. The stuff generally grows in the toilet tank – a place many people forget to clean and disinfect regularly. Toilet tanks concealed in the wall are also more difficult to clean compared to regular tanks – so even if you remember to clean them regularly, you might fail to scrub all spots and corners. 

In addition to smelling like stale water or rotten eggs, sulfur bacteria also give a grey hue to the water. As you flush, the grey residue can stain the toilet bowl.

Water Sediment

Sediment in water – different from the minerals in hard water – can also stain the water closet grey. This generally happens after a flood, if you have well water, or due to works to the waterline if you have municipal water. These stains are generally easy to remove, and the problem will go away once the water becomes clean again. 


Orthophosphates are phosphates added by cities to the municipal water supply. This anticorrosive agent is added to protect water heaters and pipes, but it can leave grey residues. 

Grey sediment due to phosphates in the water can be hard to remove if you don’t act promptly. Scrubbing the toilet with a brush once or twice a week can help you prevent it.

Is Grey Water Dangerous?

Grey water in the toilet is not necessarily dangerous, but it has the potential to carry bacteria. For this reason, you should disinfect your toilet with bleach regularly.

To Finish

Using the bathroom could feel grim when the toilet bowl has grey sediment in it. There is no need to lose hope, though. We hope this guide can help you get rid of the stains and understand what’s causing them so that you can prevent future accumulation. 

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