Can You Use Filtered Water in a CPAP Humidifier?

An Opinion Piece by Sebastian Cardenas, Founder of CSpring

As a long-term CPAP user, I've spent years dealing with one of the most common practical questions surrounding humidification: what kind of water should you put in a CPAP water chamber?

Distilled water is commonly recommended because its extremely low mineral content helps reduce deposits inside humidifier chambers. But the answer is not necessarily identical for every CPAP machine or every water chamber.

The most important rule is simple:

Follow the water instructions provided by the manufacturer for your specific machine and humidifier chamber.

Not Every CPAP Water Chamber Has the Same Requirements

One detail that is sometimes overlooked is that water requirements can differ even between chambers designed for the same CPAP machine.

For example, ResMed's current AirSense 11 instructions distinguish between two HumidAir 11 water tubs:

• HumidAir 11 Standard water tub: ResMed instructs users to use distilled water only.
• HumidAir 11 Cleanable water tub: ResMed permits drinking-quality (potable) water.

That distinction is important. It means there isn't necessarily one universal water recommendation that applies to every CPAP humidifier chamber.

Always identify the exact chamber you are using and follow its manufacturer's instructions.

Why Distilled Water Is Commonly Recommended

The primary practical advantage of distilled water in a humidifier chamber is its very low mineral content.

When water evaporates, dissolved minerals can remain behind. Over time, those deposits may appear as:

• White residue
• Scaling
• Cloudiness
• Deposits on the chamber's metal or plastic surfaces

Using distilled water can substantially reduce this mineral buildup.

This can make routine chamber maintenance easier, particularly in areas with hard water.

My Experience With Filtered Water

For many years, I personally used filtered water in my CPAP humidifier, including bottled filtered water and water from a refrigerator filtration system.

In my experience, it worked adequately, but there was a noticeable tradeoff: mineral buildup.

Living in an area with relatively mineral-rich water, I would periodically notice light deposits developing in the humidifier chamber. That meant the chamber required more frequent maintenance than I would expect when using distilled water.

That's my individual experience—not a recommendation that other CPAP users disregard their equipment instructions.

Today, I think the more useful lesson is that the manufacturer's requirements for the specific water chamber matter more than a blanket statement that every CPAP humidifier must use the same type of water.

Filtered, Purified and Distilled Water Are Not the Same

These terms are sometimes used interchangeably, but they describe different things.

Distilled water has undergone distillation, which removes most dissolved minerals.

Purified water has undergone a purification process that may include reverse osmosis, distillation, deionization, or other methods.

Filtered water has passed through a filtration system, but depending on the type of filter, substantial amounts of dissolved minerals may remain.

Bottled drinking water can also contain naturally occurring or intentionally added minerals.

This matters primarily because greater mineral content can mean more deposits inside the humidifier chamber.

What About Potable Water?

If your CPAP manufacturer specifically permits drinking-quality or potable water for your particular humidifier chamber, follow those instructions.

ResMed, for example, currently permits drinking-quality water in the AirSense 11 HumidAir 11 Cleanable water tub, while specifying distilled water for the Standard water tub.

That is a much more useful distinction than simply saying that filtered water is either universally “safe” or universally prohibited.

Mineral Buildup When Using Water Containing Minerals

If your equipment permits potable water, some mineral buildup may still occur depending on the water source.

ResMed recommends routine cleaning of its humidifier tub and currently instructs users to wash it with mild dishwashing liquid or, for the appropriate tub, soak it in a solution of one part vinegar to nine parts room-temperature water, followed by thorough rinsing.

Always follow the instructions supplied with your particular chamber rather than using an unapproved descaling or cleaning method.

When Traveling

Water availability can become more complicated when traveling.

Rather than guessing, check the instructions for your specific humidifier chamber before your trip. If distilled water is required, use distilled water whenever reasonably available. If your particular chamber permits drinking-quality water, follow the manufacturer's requirements regarding potable water.

The Bottom Line

My own experience taught me that filtered water can result in considerably more mineral maintenance than distilled water.

More importantly, however, current manufacturer instructions demonstrate that water requirements can vary depending on the particular humidifier chamber.

For the AirSense 11, for example, ResMed currently specifies:

Standard HumidAir 11 tub → distilled water only.

Cleanable HumidAir 11 tub → drinking-quality (potable) water is permitted.

So rather than relying on broad internet advice about “CPAP water,” identify your exact machine and water chamber and follow the manufacturer's current instructions.

Disclaimer

This article reflects my personal experience as a long-term CPAP user and is provided for general educational purposes. It is not medical advice and does not replace the instructions supplied by your CPAP equipment manufacturer or advice from your healthcare provider.