Skip to Content

Black Residue In Bathtub: 8 Common Causes And How To Fix Them!

Black Residue In Bathtub: 8 Common Causes And How To Fix Them!

If you’ve noticed black residue in your bathtub it can be very concerning, but luckily it is usually quite easy to identify what is causing it.

The black residue is generally caused by mineral deposits from the water filling your tub. In most cases, this can be solved by testing your water and identifying whether it is a problem on your supplier’s end or yours. In other cases, the residue can be caused by mildew, dust build-up as well a variety of different reasons that we will explain in this article.

Let’s take a look through 8 of the most common reasons for black residue in bathtubs so you can get your issue solved quickly.

8 Common Causes Of Black Residue In Bathtub

While mineral deposits are usually the culprit, there are a lot of different reasons for black residue in your bathtub.

1. Mineral Deposits

Tap water contains a variety of different minerals including calcium, magnesium and copper.

Depending on where you live and who your water supplier is the content of your water can change drastically. If your water is higher in certain minerals such as iron or manganese then these are likely to leave behind a black residue.

2. Mildew

Mildew is a common reason for black residue in bathtubs, especially if you aren’t using your bathtub regularly.

Over time, Mildew will turn black, and since it thrives in relative humidity levels between 62% and 93% a bathtub is the perfect place for it to grow. Bathtubs that aren’t being used often need to be checked over once a week or two to check for signs of mildew developing.

Mildew won’t cause permanent damage to the bathtub surface though, and it can be cleaned with household cleaning products so you shouldn’t worry if this is the case.

3. Dust Build-Up

Sometimes black residue in a bathtub can simply be caused by dust.

While dust is usually gray in color, it can also be black in some cases where homes have poor ventilation. Dust will also collect with any smaller particles that are left behind after using the tub which can also make the color darker.

This is again another case of keeping your bathtub clean if it isn’t regularly used.

4. Damaged Water Pipes

When it comes to water pipes they only last so long before they can start to degrade and become damaged.

In this condition small pieces of the pipe can break off and come out of the faucet, leading to black residue building up in some cases.

5. Water Heater Problems

Water heaters are prone to corrosion, and when this happens you may notice black specks when you run hot water.

These black specks can build up over time and leave behind a residue in your bathtub. The average lifespan of a heater is around 10 years, so if your heater is around this age it may be time for a replacement.

6. Filtration System

Most homes don’t have water filters for bathwater, but they are necessary for some areas depending on the water quality.

These filters use granulated activated carbon (GAC), which appears as tiny black specks in your water. If the filter is damaged the GAC can make its way into the water and onto the bathtub, eventually causing a black residue.

7. Drain Stopper Damage

Quite a lot of bathtubs have drain stoppers that are made using rubber.

Now, while rubber is quite durable as a material, it is prone to wear and tear over time. As it starts to wear down it can leave black deposits in your bathtub as the rubber starts to break away.

Rubber drain stopper in a bathtub

My bathtub uses a rubber drain stopper that needs to be replaced when it becomes worn

If you have a rubber drain stopper then it is worth checking that for any signs of damage if you are having problems with black residue.

8. Sand/Silt

This one is a lot less common but applicable to homes where the water is sourced from a private well.

Well water can contain small amounts of sand or silt, and while this isn’t harmful to your body it can cause black residue in bathtubs. It can also lead to issues with other appliances as well so it is important to check your filter or liner for damage.

How To Prevent Black Residue In Bathtub

Learning how to prevent black residue in your bathtub is just as important as understanding where it came from in the first place.

We’ve laid out some tips below for preventing residue in an order that will allow you to troubleshoot what the actual problem is.

Clean Regularly

The first thing you should do is start cleaning your bathtub more regularly if you don’t already.

This will quickly determine whether the black residue is a result of mildew or dust, or if there is a more fundamental issue at play. If you want to know how to clean the residue quickly, skip over to the next section of this article.

Replace Drain Stopper

Once you’ve cleaned check your drain stopper to see if it uses any rubber, and if there is any damage to it if it does.

Consider replacing the stopper if it shows any sign of wear and tears to prevent the rubber from ending up in your bathtub. If you can find a replacement that contains no rubber then this will be an even better option.

Test Your Water

The next step in preventing and determining the source of black residue is to test your water for minerals and other impurities that may be causing black residue.

There are loads of different kits for this available online and in some hardware stores, just make sure you choose one that tests for a complete profile of contaminants and minerals.

Once you have received the test results you can assess whether you need to contact your water supplier or not. High levels of iron and manganese are usually responsible for black specks in water leading to residue in your bathtub, but this can happen even within regulated limits.

Consult With A Plumber

If the black residue persists it is likely due to a problem with the water pipes, heater or a filter problem.

A plumber will be able to assess the situation and make the necessary repairs to prevent black residue from forming in the future. If the problem persists then your water is likely to contain a high amount of minerals like iron that are characterised by black specks.

How To Clean The Black Residue

Luckily, removing the residue is super easy – all you need is undiluted white vinegar with at least 5% acetic acid, one of our personal favorite DIY cleaning agents.

Using vinegar of this concentration will ensure that any mildew is removed properly (if the residue is caused by mildew), and it will also give the surface a well-deserved clean:

  • We recommend improving circulation in the cleaning area by opening windows. You should also wear a mask as there is a risk that the residue may be mildew.
  • Apply the vinegar to the black residue using a spray bottle generously and let it sit for at least one hour, making sure the drain stopped is closed to prevent the vinegar from draining away.
  • Use a non-abrasive scrubber to scrub the area thoroughly.
  • Use an old rag to wipe the area down and then rinse it through with clean water from the tap, wiping again afterwards.

Final Thoughts

The black residue is commonly caused by minerals within your water, and this is something that you can’t change easily unless you install a filter.

If you troubleshoot using the points in this article you will be able to get to the bottom of the source of black residue, and hopefully, it will be something that you can prevent in the future. Black residue is also super easy to clean, and you’ll have no problems removing it in short notice using the guide above.