CPAP Rainout: Why Water Collects in Your Tube and How to Stop It

What causes rainout

Your humidifier warms and moistens the air. As that air travels through tubing in a cooler bedroom, it cools, and the moisture condenses into droplets, just like water forming on a cold glass. The colder the room and the higher the humidity setting, the more rainout you get.

You might hear gurgling in the tube, feel droplets on your face, or find the mask wet in the morning.

Fixes that tend to work

• Use heated tubing if your machine supports it, and raise the tube temperature a notch.
• Lower the humidity setting slightly. Small steps, a few nights each.
• Insulate the hose with a fabric tubing cover, or run the hose under your blanket so it stays warm.
• Keep the machine lower than your head, for example on the floor or a low shelf next to the bed, so water drains back toward the machine instead of into the mask.
• Warm the bedroom slightly if it is very cold.
• Use your machine's automatic climate mode if it has one.

Do not overfill the chamber

Fill the water chamber only to the max line and never fill it while it is attached to a running machine. Overfilling can let water spill into the machine or the tube. Empty leftover water each morning and let the chamber dry.

Where to place the machine

Gravity helps. If the machine sits on a nightstand higher than your head, any condensation runs downhill into your mask. Placing it at or below mattress level lets water drain back toward the chamber instead. Make sure the tubing still reaches comfortably without pulling on the mask, and keep the machine on a stable, flat surface away from curtains or bedding that could block its air inlet.

When it is not rainout

If you find water in the tube even with the humidifier off, the chamber may be damaged or seated incorrectly, so check it and contact your DME. If you smell anything unusual or see visible mold in the tubing, replace it and review your cleaning routine.