CPAP Rainout: Why Water Collects in Your Hose and Mask

Quick answer: CPAP rainout is condensation inside the tube or mask. Warm, moist air from the humidifier meets a cooler hose or room, and water collects. It can cause gurgling, a wet mask, and sudden leaks. A heated hose, a lower humidity setting, a warmer room, or a hose cover usually fixes it.

Why water appears in the hose

Your humidifier adds moisture to the air so your nose and throat do not dry out. Warm air holds more water vapor than cool air. When that warm, moist air travels through a cooler tube, it releases water, the same way a cold glass sweats on a summer day.

Rainout is more likely when:

• The bedroom is cold
• The humidifier is set high
• The hose is long and uncovered
• The machine sits below the bed, so water runs toward the mask
• You use a non-heated hose in winter
• The water chamber is overfilled

Fix it in this order

1. Add or turn up a heated hose

A heated hose warms the air all the way to the mask and is the most reliable fix. If your machine supports one, check that the setting is on and the hose is fully connected. Some machines automatically reduce humidity when the heated hose is off.

2. Lower the humidity a step

If you wake with water in the mask but your nose feels fine, reduce humidity by one setting. Change one setting at a time and give it a few nights. Do not turn humidity off completely if it makes you congested or dry.

3. Warm the room or cover the hose

A hose cover insulates the tube and reduces condensation. Keeping the bedroom a little warmer helps too. Do not put the hose under the blankets; that can make the condensation worse when the air cools at the mask.

4. Raise the machine

Place the CPAP at or slightly below mattress height, not on the floor. If water collects, it should drain back toward the machine rather than into your face. Keep the hose from sagging into a low loop where water can pool.

5. Check the water chamber

Do not fill above the maximum line. Use distilled water when the manufacturer recommends it. Empty and dry the chamber each morning if your manual says to.

What rainout does to therapy

Water in the mask can cause a seal break, a sudden rush of air, and a wake-up. Gurgling in the hose is noisy and can keep you awake. Repeated rainout can make you avoid CPAP even when your breathing is well treated.

It is not dangerous to breathe humidified air, but water in the machine's electronics is a different matter. If water gets into the machine, unplug it, empty the chamber, and let it dry according to the manual. Do not use a wet machine.

Rainout versus a leak

A leak usually sounds like a steady hiss at the mask or a dry-eyed morning. Rainout sounds like gurgling or popping in the tube and may leave droplets on your face. Both can wake you, and both can coexist.

If the mask is wet only near the vent, condensation is likely. If water sprays from the mask, the chamber may be overfilled or the hose may be routed uphill.

Travel and camping

In a tent or hotel room, the air can be cold and humid. A travel CPAP with a heated hose, a hose cover, and a lower humidity setting helps. Battery-powered travel machines may not run a heated humidifier at all; in that case, use passover humidity (water in the chamber without heat) and accept a drier night.

If you are flying, empty the water chamber before security and pack it according to the airline's rules. Our guide to CPAP therapy covers equipment basics, and CPAP supplies near you can help you find a heated hose that fits your machine.

When to call your supplier

Call if water appears inside the machine, the heated hose does not warm up, the chamber leaks, or rainout continues after you have tried a heated hose and lower humidity. A cracked chamber or a damaged hose seal is a replacement issue, not a settings issue.

Heated hose settings

Most heated hoses have a temperature setting separate from humidity. A higher hose temperature keeps water vapor from condensing. If your machine has automatic climate control, it may adjust both together. Read the manual or ask your supplier which setting is which.

If you still get rainout, check that the hose is not covered by a blanket and that the machine is not placed near a cold window.

Frequently Asked Questions

Is CPAP rainout dangerous?

Breathing humidified air is not dangerous, but water inside the machine can damage electronics. Unplug and dry the machine if water gets inside, and do not use it wet.

Does a heated hose stop rainout?

It is the most effective fix for most people because it keeps the air warm to the mask. You may still need to lower humidity in a very cold room.

Why does my CPAP hose fill with water only in winter?

Cold room air cools the hose faster, so moisture condenses inside. A hose cover, a warmer room, or a heated hose usually solves it.

Should I turn off the humidifier to stop rainout?

You can lower it, but turning it off may cause dryness and congestion. Try a heated hose and a one-step reduction first.

Can I use tap water in my CPAP?

Follow your machine's manual. Many manufacturers recommend distilled water to reduce mineral buildup. Tap water is not an emergency, but it can leave deposits.

What if water gets into my mask?

Take the mask off, empty the hose, and dry the parts. Check that the machine is not above your head and that the chamber is not overfilled.

This article is general information, not medical advice. Symptoms, testing, and treatment decisions depend on your own history, so talk with a clinician who can evaluate you.

Related reading

• CPAP therapy: getting started
• CPAP supplies near you