What is the brown stuff in my dehumidifier?

A dehumidifier is a great tool for removing excess moisture and humidity from the air, but it also collects dirt particles and other impurities. You should be careful about drinking water straight out of your tank because you might notice brown slime gathering in there!

This brown stuff in your dehumidifier is a combination of all the dirt, mold, and bacteria that your dehumidifier collects. This can happen when water is left sitting in the tank for long, creating the ideal environment for mold and other potentially harmful microorganisms to grow. If you don’t clean the tank, the mold feeds off of the dust and dirt, allowing it to spread. Mold can come in many different appearances, but perhaps the most common is a dark brownish to black color. If you find this brown stuff in the tank or any other part of your dehumidifier, it’s time to clean and disinfect it.

Below, we’ll talk about some different things that might cause the buildup of brown stuff in your dehumidifier, and then we’ll offer some tips that will help you take care of the problem.

Why Does my Dehumidifier Have Brown Stuff in It?

If you see brown stuff in your dehumidifier bucket, filter, or any other part of the unit, there is a high chance that this comes from a mix of mold, dirt, and bacteria collected from the air.

Your dehumidifier works by cooling down the moist air to the point that it condenses into water on the cold coils. Then, the water formed drips into the dehumidifier bucket. Although most dehumidifiers have a filter to catch dust and dirt before the air enters the unit, mold spores, bacteria, and other tiny particles are small enough to squeeze through and settle on the coils, in the water tank, or on the filter itself.

When the water tank is full, the dehumidifier will automatically stop running. Then, you have to empty the tank to resume operation. If you leave the water in the tank for several days without draining it, the water will create an excellent environment for the growth of mold, mildew, and microbes.

If you have an accumulation of dust or dirt on the filter or tank, the mold feeds off these particles, forming the brown slime you can see. So, you not only need to empty the tank regularly, but you should also clean the tank, the filter, and even the exterior of the unit where dust can settle.

How to Clean Your Dehumidifier

Basic Cleaning Tools

You can prevent the buildup of brown stuff in a dirty dehumidifier with proper care and maintenance. This includes frequent cleaning of the appliance. Dehumidifiers typically require very little maintenance and the most you have to do is clean the tank every week or two and the filter at least every month. Each dehumidifier comes with specific instructions in the manual, but here is the basic process you can follow to clean your unit.

First, you will need some gloves so you don’t touch any of the mold directly. If you’re asthmatic or have allergies to mold spores or dust, you should also be careful not to inhale any of them while cleaning your dehumidifier. Wear a dust mask to be safe. Other items you will need for cleaning are a sponge or damp cloth, detergent, and bleach or white vinegar for disinfection.

When you’re ready, the very first thing you must do is turn off and unplug the unit. Do not attempt to remove or disassemble any part of the dehumidifier while it’s still plugged in, especially while it’s still running. You do not want to get any water near electric cords and sockets.

wiping off the dust or grime

You can start cleaning by wiping off the dust or grime collecting on the exterior of the unit. You can use a dry cloth for this, or a damp rag for particularly dirty surfaces. However, be careful not to spray any water directly on the unit.

Now, you can clean the water tank. Remove it from the dehumidifier, usually on the front or side of the unit. Be careful not to spill any water and then empty it into a drain or sink. Wash it with hot water and mild dish soap. Fill it half full, stir it around to remove any debris, then scrub each corner with a sponge or cloth. 

Alternatively, you can clean the tank with a solution of bleach or white vinegar for more thorough disinfection. Just mix a gallon of water with half a cup of bleach to create a simple cleaning solution.. Fill the tank with this solution until all the parts with the brown stuff in them are covered. Let the diluted bleach solution sit in the tank for 15 to 20 minutes then empty the water. Clean the tank with warm water and a soft cloth, then rinse it well, dry it, and place it back into the dehumidifier.

You may also use white vinegar to disinfect the areas affected by mold. First, empty the tank. Fill the tank with the white vinegar until all the brown stuff is covered or spray a solution of vinegar and water directly on the infected areas. Let it sit for at least ten minutes. Do not mix the vinegar with other cleaning solvents including bleach. Do not worry about the vinegar smell as it will dissipate after a while. Empty the tank again, then rinse and dry.

Lastly, make sure to clean the filter at least once every month. Remove the filter from behind the air intake and wash it directly with water until all the dust and dirt are removed. Because it’s reusable, be careful not to tear the filter. If it’s too worn out, you may need to replace it with a new one. Follow the manufacturer’s instructions for filter cleaning or replacement.

Dehumidifier Filter

How to Prevent Brown Stuff From Accumulating in Your Dehumidifier

Prevention is always better than cure, and you can easily prevent the brown stuff from collecting in your dehumidifier with proper and timely maintenance. 

Pour Out the Dehumidifier Tank When Not in Use

It’s important to empty the water tank as soon as you can. For one, you can’t use the dehumidifier when the tank is full of water. More importantly, stagnant water creates an ideal environment for mold, dust mites, and bacteria to grow inside the dehumidifier tank. 

If you are planning to leave home for a few days or are simply not using the dehumidifier, make sure to empty the tank and clean it well. If you’re out for long and have left the water in the tank unintentionally, just empty it as soon as you can and clean the tank with soap. The longer you leave the water sitting in the tank, the more likely it is to form mold, spreading spores into the air you breathe.

If you’re using the tank to collect water from your dehumidifier regularly, you should not only empty it but also rinse it after every use. Every few days or after a week, clean it with soap or disinfect it with a bleach solution or with white vinegar to kill mold and bacteria.

Draining Options of a Dehumidifiers

Choose a Unit with Continuous Drainage

If you simply don’t have the time to empty the water reservoir and clean it regularly, then you may opt for continuous drainage. This ensures that your dehumidifier will run continuously without any worries of water overflow. Most dehumidifiers have the option to connect a drain hose for continuous draining via gravity. Some models may come with a drain hose for this option, but usually, you can use a standard garden hose. 

Connect the drain hose to the outlet on the dehumidifier then direct the hose toward the drain below the unit. Make sure the hose is not bent or twisted, which can block the water flow and cause leaking, and that the unit is elevated from the drain to let the water flow down smoothly.

If you use this continuous draining option, you should also clean the hose at least once every month. There may be an accumulation of mold or dirt in the hose especially if there’s always standing water around it. You can clean the hose by pouring the vinegar/water solution and flush it down the entire length of the hose. You should also still check the tank and clean it in case any water gets inside.

Avoid Placing the Dehumidifier Near Dusty Surfaces

While there will always be dust and dirt even inside a well-kept home, you can help prevent brown stuff from accumulating in your dehumidifier by simply avoiding putting the unit near dusty places. When operating, you should keep all windows and doors closed to avoid outside air and all its dirt from getting in.

In particular, if you’re running the dehumidifier in your basement, you’ll want to keep it far from dusty tools or equipment you use outdoors. For example, if you have a storage of farm tools in the same space, the dust or dirt can get in the air and stuck in your dehumidifier’s air filter. This can also get sucked into the unit and down the dehumidifier tank. If you have no other place to put these things, make sure to also keep them clean and put your dehumidifier as far away as possible from such objects.

Clean or Change the Filter

As your dehumidifier’s primary protection against air contaminants, the filter absorbs most of the dust and dirt so that they don’t get into the internal components. If the filter is clogged with dirt and other particles, it can contaminate the water in the tank. Most dehumidifiers have a filter indicator on the panel to remind you to clean the filter after 250 hours of use or approximately a month. 

Most dehumidifiers have washable and reusable filters for easy cleaning and maintenance. Check the user manual for specific instructions before removing your filter. Some can be accessed by removing the air intake grille first, while others simply slide out from the top of the unit. You can simply wash it with water or use a vacuum cleaner with a soft brush attachment. 

Be careful when washing and drying the filter or the mesh can get damaged or torn. When this happens, you’ll need to replace the filter. After cleaning, let the filter air dry for a few minutes, then wipe it with a dry cloth before placing it back into the dehumidifier.

Protect furniture and structures


Dehumidifiers typically only require easy maintenance you can do every few weeks. If you find brown stuff in your dehumidifier, it’s likely a combination of mold, dirt, and other microbes from the air. You can easily clean your dehumidifier from this brown slime by following the basic steps we detailed above. A similar approach can be done for any warm mist or cool mist humidifier with a dirty tank or filters. Try to use distilled water instead of tap water to avoid mineral deposits on your humidifier.

Performing a regular cleaning routine and maintenance for your appliance is the best prevention and protection against potentially hazardous effects. Keeping your dehumidifier clean starts with emptying and washing your tank after every use to reduce the risks of mold growth. Over time, dust and dirt will settle on the exterior of your dehumidifier, especially on the filter. Make sure to keep all parts of the dehumidifier clean at all times.

Related Articles