What Kind of Water Goes in a CPAP Machine? Best & Worst Options

Why Does Tap Water Cause Problems in a CPAP?

The problem isn’t necessarily something you can see when you pour tap water into the chamber.

It’s what’s dissolved in it.

Tap water contains minerals such as calcium and magnesium. When water evaporates inside your CPAP humidifier, those minerals don’t evaporate with it.

They stay behind.

Over time, they can form the same white, crusty buildup you might have seen inside a coffee maker or around a faucet.

That buildup is called scale.

Scale makes the water chamber harder to clean. Depending on the chamber and how it’s maintained, mineral deposits can contribute to discoloration, pitting, corrosion, and deterioration.

ResMed specifically identifies mineral deposits as something that should be removed during water-chamber maintenance. It also recommends replacing chambers that become cracked, cloudy, or pitted.

That doesn’t mean every white deposit will clog the machine itself. But it explains why manufacturers care about the water you use.

Distilled water largely avoids mineral scale because most of those dissolved minerals have already been removed.

And there’s another issue besides minerals: water can contain microorganisms. We’ll get to that shortly.

I’ve Been Using Tap Water. Have I Already Ruined My CPAP?

Maybe you’ve been using tap water for months or years and just discovered that it could cause problems.

So, have you already damaged your machine?

Not necessarily.

Mineral buildup usually develops over time, and white residue in the water chamber doesn’t automatically mean the machine is ruined.

Here’s what to do:

1. Inspect the removable water chamber. Look for white deposits, cloudiness, discoloration, cracks, or pitting.
2. Clean it according to your manufacturer’s instructions. Some chambers can be descaled using diluted vinegar, but follow the procedure for your model.
3. Don’t try to clean inside the CPAP machine. Never pour vinegar, water, or cleaning chemicals into the machine’s internal components.
4. Use the water specified for your chamber going forward.
5. Contact your equipment supplier if something isn’t working properly. Error messages, unusual noises, or humidifier problems deserve attention.

If the machine is operating normally, that’s encouraging. But you can’t determine the condition of every internal component simply by looking at the chamber.

What If I Keep My CPAP Clean? Can I Continue Using Tap Water?

This is a reasonable question.

If minerals are the problem, why not clean the chamber every day?

Regular cleaning really does help. It removes deposits before they become thick and stubborn.

But cleaning doesn’t prevent minerals from entering the chamber every night. And it can’t necessarily reverse corrosion or damage that has already developed.

Here’s something important: not every CPAP chamber has the same water requirements.

For example, ResMed’s AirSense 11 has two different humidifier tubs:

• HumidAir 11 Standard tub (white thumb grip): Distilled water only.
• HumidAir 11 Cleanable tub (gray thumb grip): Drinking-quality water is permitted.

These distinctions appear in ResMed’s AirSense 11 user guide.

So there are circumstances where tap water is permitted with appropriate maintenance.

But if your chamber requires distilled water, keeping it clean doesn’t change that requirement.

The CDC explains that germs can grow in CPAP humidifiers and connected equipment. It recommends following the manufacturer’s instructions for water, cleaning, and maintenance.

So what if you’ve already been using tap water?

That doesn’t automatically mean you’ve become sick. Using tap water isn’t proof that you’ve developed an infection.

However, waterborne respiratory infections are possible, and people with weakened immune systems or certain lung conditions may be more vulnerable.

If you’re experiencing unexplained fever, coughing, or breathing difficulties, contact a healthcare professional.

And whether you’ve experienced symptoms or not, use the recommended water and cleaning procedures going forward.

This is a comparison of water characteristics, not a universal safety ranking. Each type has its own limitations.

1. Reverse-Osmosis Water

Reverse-osmosis water is probably the most interesting alternative because so many people already have it at home.

You’ve probably seen the refill stations where people fill three- or five-gallon drinking-water jugs.

Many of these systems use reverse osmosis to remove most dissolved minerals and other impurities.

That means properly treated RO water usually has much less potential for mineral buildup than hard tap water.

But here’s the catch.

Some drinking-water companies add minerals back after purification to improve the taste.

Those added minerals may be desirable in drinking water, but they can contribute to the deposits we’re trying to avoid in a CPAP.

RO water also isn’t necessarily sterile. Storage tanks, refill stations, and reusable jugs need proper maintenance.

So low-mineral RO water may reduce scale, but it isn’t automatically an approved substitute for distilled water.

What About Crystal Springs Reverse-Osmosis Water?

Crystal Springs is a bottled-water brand used by households and offices in many areas, including customers who buy large drinking-water jugs.

The company offers several varieties, including purified water, spring water, distilled water, and purified water with minerals added.

That distinction matters.

In a published Crystal Springs water-quality report, its purified water had a typical total dissolved solids (TDS) measurement of 5 parts per million.

Its separate purified-with-minerals-added report listed 22 parts per million.

These are published typical analyses, not guarantees for every bottle or every production location.

They illustrate why two products from the same brand can have different mineral contents.

If you already have Crystal Springs water, check exactly which variety you’re buying.

Don’t assume every jug contains the same water or that every purified product is free of added minerals.

You can compare the company’s published water-quality reports.

And if your CPAP requires distilled water, even very low-mineral RO water doesn’t automatically meet that requirement.

2. Purified Bottled Water

The word purified sounds like it should settle the question.

Unfortunately, it doesn’t.

Purified bottled water may be treated through reverse osmosis, distillation, or other processes.

Some manufacturers then add minerals back for taste.

So two bottles labeled purified water may have different mineral contents.

The treatment process and any added minerals matter more than the word on the front of the bottle.

3. Filtered Tap Water

What about water from your refrigerator filter or a filtered pitcher?

It may taste better, but that doesn’t necessarily mean it contains fewer minerals.

Many ordinary household filters reduce chlorine taste, odors, and selected contaminants without removing most dissolved calcium and magnesium.

So filtered water can still leave scale behind.

A specialized reverse-osmosis filter is different from an ordinary carbon-filter pitcher.

4. What If I Boil Tap Water First?

This is an easy mistake to make.

After all, boiling is a familiar way to make water safer to drink.

And boiling does kill many microorganisms.

But boiling doesn’t remove the dissolved minerals that cause scale.

When water boils, some of it escapes as steam. The minerals stay behind in the pot.

To make distilled water, you would have to collect that steam and condense it back into liquid water.

Simply boiling tap water and letting it cool doesn’t do that.

Boiling may address certain microbial concerns, but it doesn’t turn tap water into distilled water or override your CPAP manufacturer’s instructions.

5. Spring Water and Mineral Water

Bottled spring water sounds like a clean alternative.

But spring water naturally contains dissolved minerals, sometimes in substantial amounts.

Mineral water contains minerals by definition.

Those minerals may contribute to the taste people enjoy, but they can also contribute to scale inside a humidifier.

Being bottled doesn’t necessarily make water better for your CPAP.

6. Regular Tap Water

Tap water is convenient and generally safe to drink when supplied by a properly maintained public water system.

But the mineral content varies depending on where you live.

Some places have soft water. Others have hard water that quickly leaves deposits on faucets and appliances.

Harder water generally means greater potential for scale.

And even soft tap water isn’t necessarily sterile or approved for a particular CPAP chamber.

Can I Run My CPAP Without Water?

Here’s an option you may not have considered.

Many CPAP machines can operate without humidification.

The machine supplies the prescribed air pressure used to treat sleep apnea. The humidifier adds moisture for comfort.

On compatible machines, you can turn humidification off and continue using your CPAP without adding water.

You may notice more dryness in your nose, mouth, or throat.

Check your specific machine’s instructions for whether to leave an empty chamber installed or use an approved side cover, and how to disable humidification.

For example, ResMed explains how certain HumidAir systems can operate without humidification.

Don’t assume you should leave the heating function on with an empty chamber.

Is Distilled Water Worth the Extra Cost?

After what happened with my wife’s CPAP, this is an easy question for me.

Distilled water often costs only a couple of dollars per gallon, and depending on how much your humidifier uses, a gallon can last several weeks.

Compare that with the inconvenience of equipment problems or going without your CPAP while it’s being repaired.

For us, that meant about a month without a machine that had been making a noticeable difference in my wife’s sleep.

Of course, using tap water doesn’t guarantee your CPAP will break. And using distilled water doesn’t guarantee you’ll never have a problem.

But distilled water largely removes mineral scale from the list of things you have to worry about.

For us, that’s worth the small extra expense.

Where Can You Buy Distilled Water?

Distilled water is commonly available at grocery stores, pharmacies, Walmart, and other big-box retailers.

It’s usually sold in gallon jugs.

You can also shop for it online.

Check distilled water options on Amazon.

Keeping an extra unopened gallon on hand is an easy way to avoid running out at bedtime.

How Often Should You Change the Water in Your CPAP?

Don’t assume that using distilled water means you can leave the same water in the chamber indefinitely.

Follow your manufacturer’s instructions for emptying, cleaning, drying, and refilling the chamber.

For example, ResMed advises emptying and drying the AirSense 11 humidifier tub daily, with regular cleaning of the components.

Even distilled water can become contaminated after it’s been handled or left in a used chamber.

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Sources & Further Reading

The personal experience described in this article is our own. The following official resources support the information about CPAP water requirements, cleaning, mineral deposits, and water safety.

• ResMed — AirSense 11 User Guide (PDF)
  Official water requirements for Standard and Cleanable humidifier tubs, along with cleaning instructions.
• ResMed — AirSense 11 Product and Maintenance Information
  Guidance about mineral deposits, water-chamber deterioration, cleaning, and replacement.
• CDC — Preventing Waterborne Germs at Home
  Explains why drinking-quality tap water isn’t sterile and includes specific recommendations for CPAP humidifiers.
• Philips Respironics — DreamStation Go Humidifier Manual (PDF)
  Includes manufacturer instructions for cleaning mineral buildup from a compatible water tank.
• Primo Brands Delivery — Water Quality Reports
  Published analyses for purified, mineral-added, spring, and distilled water varieties associated with its bottled-water brands, including Crystal Springs.

Note: CPAP water and maintenance requirements vary by machine and humidifier chamber. Always follow the instructions supplied with your equipment. This article provides general information and does not replace advice from your sleep-care provider.