Using RO Water In My CPAP – Is It The Best Choice?

The water reservoir of a CPAP machine holds around 11-17oz of water, which is gradually used to humidify the air while you sleep. The water in your CPAP needs to be changed daily to guarantee that you have the best night’s sleep possible – so it is important to know which type of water you should use in your CPAP.

Distilled water is the only type of water recommended for your CPAP machine. If you do not have access to distilled water then reverse osmosis (RO) water can be used as an alternative. It is important that the filters of your reverse osmosis are regularly changed to ensure minerals and bacteria are removed from the water before use in the CPAP.

Understanding why CPAP machines need a particular type of water in them, is the key to knowing when and why you can use reverse osmosis (RO) water as an alternative.

Keep reading to also learn about whether you can use bottled water, regular tap water or anything else in your CPAP.

Can RO water be used in my CPAP?

Almost all manufacturers recommend distilled water as the ONLY type of water that should be used in your Continuous Positive Airway Pressure (CPAP) machine. This is because distilled water is safe for both your health and for that of your CPAP machine.

So, can reverse osmosis (RO) water be just as safe for you and your CPAP?

During distillation, contaminants are removed by boiling the water and then cooling, condensing and capturing the clean water vapour. Distilled water is vital for CPAP machines because of two main reasons.

  1. Minerals (such as calcium and magnesium) are removed
  2. Harmful bacteria are killed

When calcium and magnesium are not removed from your water they build up as mineral deposits called scale or limescale. Scale causes damage to your CPAP and ultimately reduces its lifespan.

While any bacteria found in the water running through your CPAP can be harmful to your health, as you risk inhaling them.

Thankfully, reverse osmosis systems ARE also able to remove minerals, like calcium and magnesium, and harmful bacteria too!

In fact, the CDC says…

“Reverse Osmosis Systems have a very high effectiveness in removing bacteria”



“Reverse Osmosis Systems will remove common chemical contaminants… including calcium and magnesium”


But, does this mean RO water is okay to use in your CPAP?

Unfortunately, the problem with reverse osmosis systems is that they use a series of filters and a semi-permeable membrane to remove contaminants from water.

Unfortunately, these filters become less effective over time, which means the longer it has been since you changed ALL of your filters, the less contaminants are removed from your RO water – And there is no way of knowing how effective your reverse osmosis systems is without constantly testing the water.

Distillation, on the other hand, is never less effective. The process always involves water reaching boiling point, which means minerals are always removed and bacteria are always killed. Making distilled water the safest and best option for your CPAP.

Having said that, if you can’t access distilled water for some reason, then RO water is the next best option.

Simply consider increasing the frequency of renewing your filters and semi-permeable membrane to ensure the effectiveness of your reverse osmosis system.

Can I use bottled water in my CPAP?

Bottled water should not be used in CPAP machines, unless distilled water, RO water or purified tap water is unavailable – with distilled water the best and only option recommended by CPAP manufacturers.

There are 3 types of bottled water:

  1. Natural Mineral Water
  2. Spring Water
  3. Prepared Water

1. Mineral water is water that comes from underground sources and is naturally high in minerals – usually calcium and magnesium.

As a result, bottled mineral water leads to a build-up of mineral deposits (scale) in the water reservoir and damages the CPAP machine. Overtime this damage reduces the lifespan of the CPAP.

2. Spring water is, as the name implies, water that comes from a spring – which may be underground or at the surface.

For spring water to be sold as ‘spring water’ in the U.S it is subject to protection and with a few exceptions is not allowed to be modified or treated.

It is unclear how many contaminants or minerals are in a bottle of spring water, and the amount will vary between different brands as they are sourced at different springs. This means spring water could cause damage to your CPAP overtime, but more importantly may contain contaminants that you do not want to be inhaling.

3. Prepared water is water that can come from ANY source, including your TAP water! It can be treated in any way that will make the water meet chemical or microbiological standards.

Ultimately, prepared water is no better or different from your tap water and should not be used in your CPAP.

What happens if I use regular water in my CPAP?

Regular water, or tap water, should never be used in your CPAP.

While regular tap water is obviously the most convenient choice when it comes to filling the water reservoir of your CPAP, it can reduce the lifespan of your machine.

Regular water contains minerals that will build up overtime and damage your CPAP machine. Which is why ALL manufacturers recommend that only distilled water should be used in CPAP machines.

Thankfully, regular water is processed at water treatment plants and will not pose a health risk should you still decide to use it in your CPAP.

However, you may find yourself in a situation where distilled water is simply not an option, such as on vacation.

During these times, regular water can obviously be used in your CPAP as it does not pose a health risk, but be sure the tap water in your area is safe.

For example, if you are holidaying in a third world country and only using bottled water for drinking or to brush your teeth, then you definitely DON’T want to be putting that tap water in your CPAP.

It is then super important once you return home to thoroughly clean your CPAP machine, especially your water reservoir. You may find you need to use vinegar to clean the reservoir if mineral deposits have already begun to build-up.

What can you use instead of distilled water in a CPAP?

Distilled water is ultimately the best and safest option for your CPAP. But distilled water is expensive and may not always be available to you.

Clearly, there are other types of water and it seems sensible to think that you may be able to use one of them.

If you can’t access distilled water for a period of time then you can consider using one of these types of water:

  1. RO water
  2. Purified tap water
  3. Boiled tap water

Avoid using bottled water or well water in your CPAP. Especially well water – there have even been cases of lung disease reported following the use of well water in CPAP machines(Ref 1)!

And NEVER EVER add anything to your water.

This includes essential oils, vinegar, lemon or indeed anything else you can think of. If it is not water do not put it into your CPAP.


Always use distilled water in your CPAP, it is the ONLY water recommended by ALL manufacturers of CPAP machines, and is the safest and best option.

Never use anything in your CPAP that is not water.

Read more about water and your CPAP machine in this great post:

Reference 1: News and medical life sciences

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