Can You Use Reverse Osmosis Water in a Humidifier?

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Wondering whether you can get away with using reverse osmosis water instead of distilled water in your humidifier?

In this guide, we’ve answered the question: “Can you use reverse osmosis water in a humidifier?”

We’ve also discussed other things you may want to know, including the pros and cons of RO water in humidifiers, the best alternative to RO water for this purpose, and why cleaning your humidifier is important.

๐Ÿ“Œ Key Takeaways:

  • You can use reverse osmosis water in your humidifier as a last resort, if you don’t have distilled water available.
  • Reverse osmosis water is better than normal tap water for a humidifier because it has a low dissolved solids concentration and can improve your air quality and reduce the risk of damage to the humidifier.
  • However, RO water may still contain trace amounts of certain contaminants, and it’s not quite as pure and clean as distilled water.

๐Ÿค” Is Reverse Osmosis Water Good To Use In A Humidifier?

Yes, you can use reverse osmosis water in a humidifier as a last resort, if you don’t have access to distilled water.

Distilled water is the very best type of water to use in a humidifier because it’s the purest. However, RO water is a suitable second-best to consider because it has a very low total dissolved solids (TDS) concentration.

With that said, RO water isn’t as pure as distilled water. Water from a reverse osmosis system might still contain traces of minerals and dissolved gases, and the RO process doesn’t guarantee the removal of all microorganisms, which may lead to mineral deposits inside the humidifier and the growth of harmful bacteria and other pathogens.

ro water in humidifier water tank

โš—๏ธ What Is Reverse Osmosis Water?

Reverse osmosis water is water that has been purified with the reverse osmosis process.

During this process, water is filtered through several filtration stages. It’s also filtered through a reverse osmosis membrane, where the majority of the dissolved solids are removed.

RO membranes have very tiny pores (usually around 0.0001 microns). When water is forced at a high pressure against the membrane, the water molecules are small enough to pass through, but most impurities are too large. They’re rejected by the membrane surface and are washed away with a small amount of wastewater.

The water that leaves an RO system is almost entirely pure and should have a low TDS reading.

๐Ÿ”Ž What Happens To Water In A Humidifier?

To understand why only certain water types can be used in a humidifier, let’s take a look at what happens to the water that we use in this machine.

The most basic explanation is that water is added to the humidifier’s water tank, the machine is switched on, and water is converted into vapor and released into the air. The purpose of a humidifier is to humidify (add moisture to) dry air.

There are a few different types of humidifiers, and exactly what happens to the water depends on the machine you’re using:

  • Evaporative humidifiers – These draw moisture from a reservoir with a wick filter. An evaporative humidifier uses a fan to blow air through a moistened wick, and the evaporated water is released into the air, increasing humidity.
  • Ultrasonic humidifiers – These create fine droplets of water with ultrasonic vibrations, before releasing them into the air. An ultrasonic humidifier uses a vibrating small metal diaphragm, which breaks the water into tiny droplets that are released as a mist.
  • Steam vaporizers – These heat water until it boils and evaporates into steam. The steam is cooled slightly, then released into the air, increasing humidity levels.
  • Impeller humidifiers – These fling water at a diffuser with a rotating disk, causing it to break into very small droplets. These are then released into the air and evaporate quickly, increasing the humidity.

Regardless of the type of humidifier you own, its primary goal should be to introduce moisture into the air to alleviate dry air conditions.

As you can see, the water in your humidifier eventually ends up in the air you breathe. And that brings us to our next point: why humidifiers require pure water.

Humidifier in a room

๐Ÿšฐ Why Do Humidifiers Require Very Pure Water?

Humidifiers require very pure water to prevent harmful particles and contaminants from dispersing into the air during the humidification process. Pure water is also required to prevent the formation of scale inside the distiller’s water tank.

When water is evaporated (or turned into mist) by a humidifier, it’s not just the water (H20) molecules that evaporate. Any impurities present in the water, like minerals, salts, or microorganisms, can also be released into the air as fine particles.

These particles, once airborne, can become part of your indoor air quality, and potentially pose health risks when you inhale them.

Certain minerals and impurities in your water, like calcium and magnesium, can lead to the accumulation of scale deposits on the humidifier’s components, reducing the appliance’s efficiency and potentially causing long-lasting damage. These minerals are present in most water supplies – an estimated 90% of homes in the US have hard water.

Using pure water, which is best achieved through distillation, helps you to minimize the introduction of harmful contaminants into the air and prevent mineral buildup in the humidifier.

โš–๏ธ Pros And Cons Of Reverse Osmosis Water For Humidifiers

Let’s take a look at the advantages and disadvantages of using reverse osmosis water in a humidifier.


  • More affordable than distilled water – RO water is typically cheaper to buy in bottles than distilled water. So, if you get through a lot of water in your humidifier, bottled reverse osmosis water is the cheapest long-term option.
  • Quicker to produce at home – Reverse osmosis systems produce purified water in a matter of seconds, while water distillers take up to 5 hours to produce a single 1-gallon batch of distilled water. You’ll get access to purified water for your humidifier much more quickly from your own RO system than you would from a distiller.
  • Very low in TDS – Reverse osmosis water is much purer than filtered drinking water. It contains virtually no dissolved solids, so it’s unlikely to cause much (if any) damage to your humidifier components.
  • Improved air quality – Using reverse osmosis water instead of impure tap water in your humidifier should improve your air quality because of the lack of potentially harmful contaminants in the treated water.


  • May still contain humidifier-damaging minerals – RO water isn’t as pure as distilled water and may contain trace amounts of minerals and impurities that accumulate on the humidifier’s components, affecting its performance efficiency.
  • May also contain harmful contaminants – RO water may also still contain dissolved gases, like certain VOCs, which may end up being released as water vapor and inhaled by you, with possible negative health ramifications.
  • May leach materials from the humidifier – The RO water purification process removes minerals and ions, which makes reverse osmosis water acidic by lowering its pH. If you use an ultrasonic humidifier with a metal diaphragm, there’s a risk that the “hungry” RO water will leach metals from the machine – and you may end up breathing these in.
Filling a glass with filtered water from an RO system

๐Ÿšซ Why Isn’t Reverse Osmosis Water Completely Pure?

Reverse osmosis water isn’t completely pure because of the limitations of the treatment process.

Most reverse osmosis membranes have a pore size of around 0.0001 microns. The majority of impurities are larger than this, so they rebound off the membrane, while water molecules are small enough to squeeze through.

However, some impurities may still be able to pass through the membrane with the water molecules. This could be due to their size (for instance, some microorganisms are smaller than 0.0001 microns), or it could be due to an inconsistency in the membrane pore sizes, or degradation of the membrane that allows larger impurities to leak through. Plus, impurities that don’t have a high ionic charge and have a low molecular weight (such as many dissolved gases) can also remain in water during the RO purification process.

The limitations of the RO treatment process are largely due to the fact that it’s a physical process, while distillation is much more effective in completely purifying water because it vaporizes and condenses water rather than sending it through filtration media.

๐Ÿ”‚ Best Alternative To RO Water In A Humidifier: Distilled Water

Distilled water is the best alternative to reverse osmosis water in a humidifier. Many humidifier manufacturers state that only distilled water should be used in their machines to support performance efficiency and longevity.

Distilled water is free from up to 99.99% of all impurities. That means there’s no risk of this water source contributing to bacteria and mold growth inside a humidifier, and it won’t contain harmful contaminants that you could end up breathing in your indoor air. Plus, distilled water is mineral-free, so it won’t contribute to scale build-up in the humidifier.

You can buy distilled bottled water for your humidifier, but if you get through water in your humidifier quickly, it’s worth investing in a water distillation system. Distilling water at home is more cost-effective, not to mention better for the environment, in the long run. It also means you’ll have distilled water on hand for whenever you need it, rather than having to make a dedicated trip out or order online.

Pouring distilled water from glass container

๐Ÿงผ Why Cleaning A Humidifier Is Important

Even if you use pure, clean water in your humidifier, it’s still important to clean the unit to keep it functioning efficiently and help it to last as long as possible.

While using distilled water can significantly reduce the buildup of minerals and impurities compared to tap water, there are still several reasons why cleaning is necessary:

  • To prevent microbial growth. Even with distilled water, there can be a small amount of microbial contamination over time. Bacteria, mold, and other microorganisms can find their way into the humidifier’s reservoir and other components. You can prevent the growth and dispersal of these contaminants into the air with regular cleaning.
  • To remove residue. Distilled water may still leave behind some residue over time. This residue can accumulate on the humidifier’s surfaces and impact its efficiency. Cleaning your humidifier regularly will remove this residue and keep your humidifier working optically.
  • To prevent a buildup of dirt and dust. Airborne dust and dirt particles will gradually settle in the humidifier’s reservoir and other components, affecting the quality of the humidified air and causing the humidifier to work less effectively. You can prevent this dust and dirt from building up with a quick, occasional clean of the humidifier.
  • To ensure the longevity of the humidifier. Regular cleaning and maintenance of your humidifier help to extend its lifespan. By cleaning your humidifier you prevent the buildup of impurities that could gradually deteriorate the humidifier’s components and reduce its overall efficiency.

It’s generally recommended that you clean your humidifier every three days, regardless of the purity of the water you use in it.

To clean your humidifier, empty out the water tank, then wash it out with hot water and dish soap. You can use distilled white vinegar for a deeper clean if you notice limescale.

You should also disinfect your humidifier with a bleach or hydrogen peroxide solution at least once a month. Fill a tub with the bleach/hydrogen peroxide solution and soak the parts for 20-30 minutes, then rinse thoroughly and wipe them clean.

๐Ÿ“‘ Final Word

To recap, reverse osmosis water can be used in a humidifier – but it’s best to use distilled water, which is slightly purer and is less likely to leave limescale deposits in the humidifier’s water tank.

If in doubt, check your user manual. You should find the manufacturer’s instructions on the best water to use in your humidifier, and the maintenance and servicing that will help you to enjoy the humidifier for as long as possible.

โ” FAQ

Can reverse osmosis water in a humidifier trigger allergic reactions?

No, reverse osmosis water shouldn’t trigger allergic reactions in people that are prone to allergies from humidifiers. RO water is virtually impurity-free and shouldn’t contain impurities that could lead to mold and bacteria buildup inside the humidifier tank.

What type of water is best to use in a humidifier?

The best type of water to use in a humidifier is distilled water. Distilled water has been purified with the distillation process, which involves boiling water until it evaporates, then condensing the pure water into a separate container. The result is clean, fresh water that’s free from all dissolved minerals and TDS. Distilled water is the ideal choice for a humidifier because it doesn’t contain any contaminants that could lead to scale build-up or bacterial growth inside the humidifier’s tank.

What can I use instead of distilled water in my humidifier?

You can use any form of purified water instead of distilled water in your humidifier. A good water type of reverse osmosis water, which is free from almost all impurities and shouldn’t cause scaling or bacterial growth in your humidifier tank. However, you shouldn’t use filtered water or bottled water in a humidifier. Even bottled water that has been filtered usually has added minerals, resulting in mineral deposits inside the humidifier.

Will reverse osmosis water damage a humidifier?

No, reverse osmosis water is unlikely to damage a humidifier. However, water from a reverse osmosis system might still contain low levels of minerals, which could deposit inside the humidifier’s tank and clog the machine. That’s why it’s best to use the most purified water there is for your humidifier: distilled water.

Is distilled or RO water better for humidifiers?

Distilled water is better than RO water for humidifiers because it’s purer and less likely to contain minerals, microorganisms, and dissolved gases. The reverse osmosis process isn’t quite as thorough as distillation, so RO water may contain trace amounts of certain impurities, which might accumulate in the humidifier over time.

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