What Kind of Water Can I Use in My CPAP Humidifier?

By Lily – Registered Respiratory Therapist

The type of water you use in your CPAP humidifier is very important. Let us walk you through which water to use, which water you can use sometimes, and which water you should avoid using in your heated humidifier at all costs. 

If you use a humidifier with your CPAP machine, you probably already know that you should use distilled water to fill up the water chamber inside your humidifier. But do you know why it’s distilled water you need and not filtered, reverse osmosis, spring, or boiled water? Keep reading to see what the difference is between the different types of water and why the type of water matters when filling up your CPAP humidifier.

• Distilled Water
• Tap Water
• Spring Water
• Boiled Water
• Reverse Osmosis Water
• How to clean CPAP humidifier water chamber with mineral buildup
• How to keep water chamber bacteria and mold free
• How to clean a moldy humidifier
• Key points to take home

Distilled water is free from minerals and contaminants, such as mold spores and bacteria. Water is heated past its boiling point of 100 degrees Celsius, the vapor is captured, cooled and the condensate that forms is collected to create distilled water. 

This process removes minerals and contaminants because water has a lower boiling point than many of these impurities. And of course, boiling water kills microbes and bacteria. Water boils and then condenses, leaving behind impurities.

Distilled water is recommended for use in your humidifier because it is free from minerals and bacteria. Using water that contains minerals will cause a white chalky residue to form in your water chamber. This residue comes from dissolved minerals in the water and can become difficult to clean if allowed to accumulate.

If you are traveling and cannot find distilled water or simply ran out of it, you can use tap water for one or two nights. Please make sure to wash your water chamber thoroughly in the morning with mild soap and water to remove any potential mineral buildup. 

Using tap water for a few nights won’t damage your humidifier and shouldn’t be a cause for alarm. However, if you are in a country where tap water is not safe for consumption, we would caution against using tap water in your humidifier. 

You don’t know what kind of contaminants or microorganisms may be in the tap water, and you do not want to risk breathing in any microbes. Please consider boiling the tap water before use or look into bottled or purified water, especially if you are in a foreign country and are unfamiliar with its water quality. While boiled water is not mineral free, it is at least safe to consume.

Spring water, also called mineral water, is water from an underground source that may contain a lot of natural minerals. Spring water may or may not be bottled at the source, depending on the manufacturer. 

Some companies will collect the water in tanker trucks and bring it to a bottling facility where it is ozonated or chlorinated to prevent contamination. The water is then bottled at the facility. 

As the name suggests, spring water contains a lot of minerals which contributes to its taste. But it should not be used to fill up your CPAP humidifier tank. The exception would be if you are away from home and cannot find any distilled water for your humidifier.

When water is boiled, it kills off bacteria and microorganisms, making it safe to drink. However, minerals remain in the water, so boiled water is not ideal for your humidifier. 

Water that has been boiled will actually have more mineral content because some water is lost as vapor during boiling. You will have slightly less water but the same amount of minerals. 

Boiled water can be used in your humidifier in an emergency if you do not have any distilled water on hand. A few nights of using boiled water shouldn’t lead to any buildup in your water tank.

Reverse osmosis is a type of water filtration method that removes contaminants by forcing water through a semipermeable membrane under pressure. There can be multiple filters in a reverse osmosis (RO) system in addition to the semipermeable membrane. 

Water runs through a carbon filter and a sediment filter prior to being forced through the semipermeable membrane which filters out particles that are too small to be seen with the naked eye. 

Minerals, chlorine, fluorine, pesticides, and sediment are removed to produce clean drinking water. Because minerals are removed during reverse osmosis, you can use RO water in your CPAP humidifier without having to worry about limescale buildup.

If you’ve been using water that hasn’t been treated to remove minerals, chances are you now have limescale buildup at the bottom of your water tank. You’ve scrubbed and scrubbed with dish soap and warm water but the residue is stubborn and won’t go away. 

A trick to removing the residue is to soak the water chamber in a vinegar water solution. One part vinegar to three parts water should be enough to descale the water tank if you let the solution sit for 30 minutes to 1 hr. 

If you find the residue is very stubborn, increase the vinegar in the solution to 1 part vinegar and 1 part water, and make sure to rinse the water tank thoroughly to remove the vinegar smell afterward. 

If this does not remove the buildup, consider purchasing a new humidifier water tank. Water tanks are relatively inexpensive, and although prices differ depending on your CPAP machine, they generally run from $20 to $50. 

Water tanks should be replaced every 6 months and cleaned at least once a week. Please use mild soap and warm water for cleaning. It is important not to use hot water as it will damage the water chamber. Also, please do not put the water chamber in your dishwasher unless the user manual specifies it is dishwasher safe.  

You can keep your water tank free from bacteria and mold by sticking to a cleaning routine and changing the humidifier water regularly. Completely empty out your humidifier tank every two or three days and replace it with new distilled water. 

This prevents stagnant, warm water from sitting in your water tank which is a breeding ground for microorganisms and mold. It is a good idea to sanitize your water chamber regularly in addition to cleaning it with soap and water. 

Sanitizing kills bacteria while cleaning removes visible dirt and impurities and reduces the number of bacteria (but does not necessarily kill them). You can sanitize your water tank by soaking it in a solution of one part vinegar to three part water or use a CPAP sanitizer that does all the work for you. 

We recommend using UV sanitizers instead of ozone sanitizers as ozone is a respiratory irritant and contributed to the Philips foam recall of 2021. 

UV sanitizers, such as the Paptizer, use UV light to kill bacteria and can eliminate 99.9% of bacteria in a few minutes, saving you time and preventing the unpleasant vinegar smell that may linger after using vinegar to sanitize your supplies.

If you notice mold growth in your water tank, you will need to deep clean your water tank, hose, and mask. Please disconnect the hose from your machine and soak the hose and mask in a solution of one part vinegar to one part water for at least 30 minutes. 

While the hose and mask are soaking, clean your humidifier water tank with undiluted vinegar using a clean cloth. You may want to use a cotton swab dipped in vinegar to get into any hard-to-reach crevices such as around the gasket seal. 

Rinse the water tank, hose, and mask with water to remove the smell of vinegar. If you notice there is still mold after cleaning, please replace the entire circuit (water tank, tubing, and mask). 

It is not recommended to use a CPAP machine that is contaminated with mold as you risk breathing in mold spores that can cause allergic reactions in sensitive individuals. These allergic reactions include headaches, coughing, sneezing, allergic skin reactions, watery eyes, nasal congestion, and sore throat. 

Long-term exposure to mold spores and mycotoxins (toxic chemicals released by some species of mold) increases the risk of developing asthma. Mold can trigger exacerbation in asthmatic individuals since it is an allergen, and people with asthma should avoid exposing themselves to mold. 

While mold will not cause allergic reactions in everyone – some people may only have a runny nose – it’s important to keep in mind that you are essentially setting yourself up for long-term mold exposure with poor CPAP hygiene. According to the Environmental Protection Agency, research on the effects of long-term mold exposure is still ongoing.

The key to preventing limescale buildup in your humidifier water reservoir is to use mineral-free water. Distilled water and reverse osmosis water are mineral free. 

A few nights of using water with minerals (bottled water, spring water, boiled water) will not harm your humidifier and should not lead to limescale buildup.

Use a solution of equal parts vinegar and water to descale your water reservoir if the residue is stubborn. If there is mold in your humidifier, clean your water tank, hose, and mask. Use undiluted vinegar to clean the moldy water reservoir. 

If you cannot remove all the mold, replace the water tank, hose, and mask. Even with regular weekly cleaning, some bacteria will remain on your CPAP equipment. Use a sanitizer to eliminate bacteria and replace equipment regularly.