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CPAP Rainout: how to manage water in the tube and keep your CPAP clean

Written by Dr. Yasmin Aghajan, MD

Reviewed by Dr. Robert S. Rosenberg, MD


CPAP (continuous positive airway pressure) works to treat obstructive sleep apnea (OSA) by blowing air into the airway with a small amount of positive pressure. This keeps the airway open and prevents upper airway collapse throughout the night. One of the important functions of the upper airway is to heat, humidify, and filter the air which enters the lungs. CPAP machines are humidified to match the normal function of the upper airway. Without humidification, CPAP could cause dry mouth and irritation of the nasal passages. Therefore, heated humidification is essential to comfortable, effective and healthy CPAP use. However, this comes with the challenge of condensation building up inside the CPAP tubing, also commonly known as “CPAP rainout.” Fortunately, there are several solutions for CPAP rainout to prevent problems arising from water in the CPAP tubing.

What is CPAP Rainout?

CPAP uses heated humidification to maintain a comfortable sleep environment, whether with a face mask or a nasal mask system. All major CPAP machine manufacturers now offer humidification. The water will condensate onto the cooler tubing, much like the condensation on a soda can on a hot day. This water can splash onto the face and become an annoyance, or remain stagnant in the tubing system and become a nidus for bacteria and mold to grow.

The Importance of Clean Tubing

Researchers evaluated the rate of infection between those who use CPAP and those who do not. A study was done1 to evaluate people with OSA diagnosed by polysomnography (sleep lab study) who used CPAP with and without humidifiers, compared to controls (people without OSA, not using CPAP). Upper respiratory infections were common in all three groups, but higher in patients using CPAP. Patients with a heated humidifier had fewer respiratory infections (22% vs. 42%), but patients who did not clean their hot water bath humidifier had significantly more infections (57% vs. 20%) compared to patients who regularly cleaned their machines and tubing. This suggests that inadequately cleaned tubing in CPAP is a risk factor for infectious diseases.

In fact, researchers have been studying the potential of CPAP humidification and its effect on bacterial growth. In one study, researchers contaminated the humidifier water of 11 CPAP devices with bacteria2. They found bacteria in the breathing tube in 9 out of the 11, suggesting that the humidifier may be aerosolizing (spreading through the air and vapor) the bacteria to the tubes. However, when they used a filter between the humidifier and the tubing, no bacteria was able to get through. Thus, a filter may be one solution in the future to prevent bacteria from spreading through the tubing.

In the neonatal intensive care unit, nasal CPAP is used to support the respiratory system of premature infants and those with breathing complications. A study was done to look at the presence of bacteria3 in the nose with CPAP use. Researchers found that nasal CPAP use was associated with increased bacterial colonization of the nose and nasal passages (nares) of the infants.

Although rare, there have been some situations where CPAP users experienced eye problems potentially related to CPAP. There have been a few reports4 by eye doctors of patients who had complications while using CPAP therapy; one woman who had gas-permeable hard contact lenses while using CPAP developed vascularized limbal keratitis (discomfort in the front of the eye due to inflammation). Another man had corneal ulcers after starting CPAP. A third person had dryness with contact lenses and then had two episodes of bacterial conjunctivitis (infection of the eye). Doctors cannot say for sure that those complications are due to CPAP, but users must be aware of their eye health and especially consult with their optometrist or ophthalmologist before using CPAP if they have eye conditions or wear lenses. Humidification and cleaning of the inner tubing can help prevent some of the problems arising from dryness, as well as reduce the risk of infections near the nose and eyes.

Solutions to CPAP Rainout

There are some measures that can be taken at home with your CPAP device to prevent CPAP rainout.

  1. Lower the CPAP machine below your mask. This prevents condensation from flowing to your face, and allows it to drain via gravity back towards the humidifier.

  2. Wrap the tube to keep the air warm. There are special tube wrappers to insulate the air, keeping it warm and preventing condensation. Some people sleep with the CPAP tubing under the bed covers.

  3. Keep your room slightly warmer. The cooler the room air, the more likely it is to have condensation in the tubing. Condensation is more likely to occur if there is a large temperature difference between your CPAP air and your room air.

  4. Adjust humidifier settings. The humidifier warms the air in the system to around 80 degrees Fahrenheit. If you already live in a humid environment, you may not need as much humidification. Talk to your CPAP equipment provider about the settings.

  5. Use heated CPAP tubing. Keeping the air warm will prevent condensation of the water into droplets. Most manufacturers of CPAP now offer heated tubing to keep the inside of the tube and the air warm. You can also purchase separate heated tubing to use with older machines.


CPAP is a home medical equipment machine and a form of non-invasive ventilation. It is an essential component of treating sleep disorders to ensure restful and healthy sleep, prevent daytime sleepiness, and treat sleep apnea. Sleep apnea, when untreated, can lead to a host of medical problems including high blood pressure, obesity, diabetes, and increased risk of heart attacks and stroke. Many people using CPAP to treat obstructive sleep apnea. The machines work by providing positive continuous airway pressure to keep the airway open and prevent apnea or hypopnea. They also have heated humidifiers to keep the air warm and prevent dryness. In this article we discussed the potential complications of water in the tube in relation to infection. Keeping the tube clean can help reduce the risk of infections related to CPAP. Talk with your sleep specialist about what you can do to optimize your CPAP to maximize its benefits.


1 Sanner BM, Fluerenbrock N, Kleiber-imbeck A, Mueller JB, Zidek W. Effect of continuous positive airway pressure therapy on infectious complications in patients with obstructive sleep apnea syndrome. Respiration. 2001;68(5):483-7.

2 Ortolano GA, Schaffer J, Mcalister MB, et al. Filters reduce the risk of bacterial transmission from contaminated heated humidifiers used with CPAP for obstructive sleep apnea. J Clin Sleep Med. 2007;3(7):700-5

3 Aly H, Hammad TA, Ozen M, et al. Nasal colonization among premature infants treated with nasal continuous positive airway pressure. Am J Perinatol. 2011;28(4):315-20

4 Harrison W, Pence N, Kovacich S. Anterior segment complications secondary to continuous positive airway pressure machine treatment in patients with obstructive sleep apnea. Optometry. 2007;78(7):352-5