A Continuous Positive Airway Pressure (CPAP) machine supports breathing by delivering pressurized air through a mask. Most modern units include an integrated humidifier, a reservoir that adds moisture to the airflow. This humidification prevents common side effects like a dry throat or nasal passages during therapy. New users often ask what type of water is safe for this reservoir. Manufacturers and medical professionals highly discourage using water straight from the faucet.
The Primary Issue: Mineral Deposits and CPAP Longevity
Tap water contains inorganic solids, primarily calcium and magnesium, which cause water hardness. When the CPAP humidifier heats the water, pure water molecules vaporize, leaving the dissolved minerals behind in the chamber. This process rapidly accumulates a chalky residue, known as scale or limescale, on the heating plate and reservoir walls.
Scale acts as an insulator, reducing the heating plate’s ability to efficiently transfer heat and lessening humidification effectiveness. This residue can also flake off, potentially clogging small air passages and filters within the device. Persistent use of hard water leads to permanent etching or clouding of the plastic water chamber, necessitating costly replacement. These inorganic deposits shorten the machine’s operational lifespan and may void the manufacturer’s warranty.
Beyond Minerals: Water Quality and Health Concerns
Even if tap water is safe for drinking, it is not sterile and poses a biological risk when aerosolized by a CPAP humidifier. Municipal water supplies contain trace levels of microorganisms, including bacteria like Legionella and non-tuberculous mycobacteria (NTM). While these pathogens are neutralized by stomach acid when swallowed, they are problematic when inhaled directly into the sensitive lower respiratory tract. The warm, stagnant environment of the humidifier tank creates an ideal breeding ground for these organisms to multiply and form biofilms.
The CPAP machine turns the water into a fine mist, or aerosol, which is delivered under pressure deep into the user’s lungs. This mechanism bypasses the respiratory system’s natural defenses, allowing contaminated water droplets to reach the alveoli. Inhaling these contaminants can lead to respiratory infections, including pneumonia, especially in individuals with pre-existing pulmonary conditions or compromised immune systems.
Distilled Water and Essential Cleaning Protocols
The recommended choice for any CPAP humidifier is distilled water, which is water that has been boiled into steam and condensed back into a liquid. This distillation process effectively removes all minerals, chemicals, and most microorganisms, ensuring the water is nearly pure. Using distilled water protects the device’s internal components and the user’s respiratory health by preventing scale and biological growth.
If distilled water is unavailable, a temporary alternative is tap water that has been boiled vigorously for at least five minutes and cooled completely. While boiling kills most microorganisms, it does not remove dissolved minerals, meaning the risk of scale buildup remains. Bottled water, including spring or purified water, also contains minerals and should only be used as a short-term substitute.
If any water other than distilled water is used, the humidifier chamber must be thoroughly cleaned afterward to remove residual mineral deposits. A weekly cleaning protocol should include soaking the chamber in a solution of one part white vinegar to three parts water to dissolve scale, followed by a thorough rinse and complete air-drying.