Why Does My Humidifier Water Turn Black?

In this article, we discuss the reasons your humidifier water turns black. 

Humidifier water turning black is a common occurrence but one that needs to be addressed immediately to avoid bigger issues down the line. These could include reduced performance, and decreased lifespan for the humidifier, and even health problems for you. 

There are a couple reasons why your humidifier water might be turning black, from using the wrong type of water, to a dirty water tank, and more. 

We live and breathe ‘humidifiers’. So if you aren’t sure about something related to humidifiers, just leave it to us. Here, we will tell you why humidifier water turns black, how to fix it, and also how to prevent it from happening. 

Keep reading for more information. 

What Causes Humidifier Water To Turn Black

There are a couple reasons why your humidifier water might turn black, but all of them have something in common. 

Specifically, humidifier water turns black due to the presence of some contaminants or foreign substances in the tank. 

But how exactly did they get there? 

Mineral Deposits

One of the most common causes for humidifier water turning black is mineral deposits. If you live in an area with very mineral rich water, using this water in your humidifier could lead to mineral deposits in the water tank, the filter, or even the nozzle. 

Minerals come in all colors, including black and other dark shades. If your humidifier’s tank has a lot of mineral deposits, these could release particles into the tank and change the color of the water. 


Humidifiers are prone to developing mold if they are not maintained properly. 

If you aren’t familiar with mold, it’s a fungal growth. Visually, it resembles furry patches of fibrous strands clumped close together. Again, mold can very easily develop in a humidifier’s water tank, in the filter, or anywhere else. 

Mold thrives in dark and damp areas, of which there are many in your humidifier. Mold comes in all kinds of colors, ranging from gray, white, and brown, to brighter hues such as yellow, orange, green, and blue. 

Some types of mold can even be black. And much like mineral deposits, mold can release particles into the water tank, making it appear as though the humidifier water has turned black. 

Dirty Water Tank

Often, the right answer is the simplest one. And in the case of humidifier water turning black, the simplest reason is just a dirty water tank. 

If the water tank of your humidifier has been exposed to contaminants like dirt and dust, it could cause these contaminants to build up over time. The result is humidifier water that appears black, or just a dark shade of brown. 

Why Humidifier Water Turning Black Is Bad

We shouldn’t need to answer this question, but it’s important that you know all the risks involved with black humidifier water. 

If your humidifier water turned black because of particles released by mineral deposits, it could spell disaster for your humidifier’s performance and longevity. 

This is because mineral build up can cause decreased mist volume, poor coverage of a space, and malfunctions with the diffuser. 

If it’s mold that’s causing your humidifier water to turn black, the problem could be even more serious. Mold can be seriously harmful for humans and animals alike. And if there’s mold in the water tank of your humidifier, it can very easily spread to the rest of your house. 

To name just a few symptoms of mold in humans, you have breathlessness and other respiratory problems, headaches, watery eyes, throat and lung irritation, inflammation, rashes, allergic reactions, and the list goes on. 

And finally, if you just have a dirty humidifier water tank, it could release dirt and dust particles into your home. Besides making your living space filthy, these could have disastrous effects on your respiratory health. 

How To Fix Black Humidifier Water

‘Black humidifier water = bad news. Got it! So how do I fix it?’

Well, as we’ve established, black humidifier water is a byproduct of contaminants in the humidifier’s water tank. So the best way to deal with it is to give your humidifier a thorough cleaning that removes all of the contaminants. 

But the method used to clean the tank will vary depending on what type of contaminants you have in your humidifier’s water tank. 

How To Clean A Dirty Humidifier Tank

If you’ve identified the contaminants in your humidifier as dirt, dust, sediment, or something of that sort, cleaning it is fairly straightforward. 

Start by emptying the water tank and removing the filter. Next, use distilled water to wash the tank. Distilled water is necessary because it lacks all and any contaminants, minerals, and heavy metals that could make the problem even worse. 

Next, use dish soap and a sponge to go over the entire water tank. If you notice some stubborn sediment deposits that just won’t budge, use a thick bristle brush to agitate them. Rinse out the whole tank, and you should be good. 

How To Clean Mold Or Mineral Deposits Out Of A Humidifier

On the other hand, if your humidifier’s tank has mineral deposits or mold in it, the cleaning process will differ slightly. You will have to do a proper descale of the humidifier. 

Start by preparing a cleaning solution of 3% hydrogen peroxide and distilled water in a 1:3 ratio. Alternatively, you could use a cleaning solution made with equal parts distilled water and distilled white vinegar. 

Next, pour the cleaning solution into the water tank of your humidifier, ensuring all of the affected areas are fully covered. Close the tank and shake the whole thing vigorously. 

Shaking the tank like this ensures that all of the affected areas are fully covered, and also helps loosen up the contaminants a bit. 

After that, just let the cleaning solution sit for a while and do its magic. We recommend letting it sit for at least an hour. 

Then, pour out the cleaning solution and inspect the tank. All of the mineral deposits or mold should have been cleared away. If there’s still some left, repeat the descaling process, but this time use a thick bristle brush to agitate the contaminants. 

How To Prevent Humidifier Water From Turning Black

Now that we know how to deal with humidifier water turning black, let’s look at how to prevent it from happening in the first place. 

We recommend doing all of the following in order to prevent your humidifier water from turning black. 

Clean The Humidifier Regularly

Regularly cleaning the humidifier prevents any contaminants from getting deposited in the water tank. This ensures continued high performance and also extends the longevity of your unit. 

To clean the humidifier, just follow the process we described above. As for frequency, we recommend cleaning the humidifier at least once a week, if not more for units that get used more heavily. 

It is also a good idea to descale the humidifier semi-regularly. The process for descaling has also been described above. For descaling, we recommend doing it at least once a month. 

By doing so, you clear away any contaminants, mold, minerals, or sediment deposits before they have a chance to accumulate and get out of hand in your humidifier’s water tank. 

Replace The Water Filter

Another essential maintenance feature of humidifiers is regular replacement of the filter. Your humidifier’s filter is designed to take a lot of abuse, but even it has a limit for how many contaminants it can eliminate. 

In fact, the filter is the second most susceptible part of your humidifier, when it comes to mold and mineral deposits. 

Some humidifiers come with a washable water filter, but most will require a replacement every 2 months or so.  

Use Distilled Water In The Humidifier 

And finally, we come to the most effective method of preventing your humidifier water from turning black. 

Using distilled water in your humidifier is the best option because it eliminates all contaminants, heavy metals, minerals, and anything else that could cause your humidifier water to turn black. 

In contrast, hard water, purified water, and even tap water contain some amount of minerals. These minerals can very easily build up in the water tank and lead to the water turning black. 

Besides being better for the humidifier, distilled water also benefits you by eliminating any irritants and contaminants that could cause health issues. 


In summation, there’s only really one reason for humidifier water turning black: a dirty humidifier. 

The only thing that varies is the substance that is contaminating the humidifier. These include mold, mineral deposits, sediment, dust, and the like. Regardless of which one you’re dealing with, they could cause serious problems for both you and your humidifier. 

Thankfully, the cure for all of these problems is the same as well: regular cleaning and maintenance of the humidifier. 

Again, you’ll have to adjust your cleaning strategy based on what the contaminants are, but the processes for cleaning are pretty similar.


Shawn Willis is all about humidifiers. After working for some of the biggest names in the industry, he started HumidifierGuys with Scott Dawson. Now, the dynamic duo helps others figure out what they need in their next humidifier.

Shawn is an avid sports fan, motorcycle enthusiast, and has two dogs named Whiskey and Boba.