Continuous Positive Airway Pressure (CPAP) therapy is a common and effective treatment for obstructive sleep apnea. A heated humidifier is often integrated into the device to add moisture to the pressurized airflow, which improves user comfort and helps maintain adherence to therapy. Manufacturers consistently recommend using only distilled water in the humidifier chamber to ensure the safety and optimal function of this medical device. This requirement stems from fundamental differences in water composition that affect both the machine and the user’s respiratory health.
The Mineral Difference Between Distilled and Tap Water
Distilled water is created through vaporization and condensation, where water is boiled into steam and then cooled back into a pure liquid form. This process effectively leaves behind almost all impurities, including dissolved salts, heavy metals, and microorganisms. The resulting water contains an extremely low concentration of Total Dissolved Solids (TDS). Tap water, in contrast, contains varying levels of dissolved inorganic minerals, most commonly calcium and magnesium. These substances, which contribute to water “hardness,” make tap water unsuitable for CPAP use because their presence causes problems when the water is heated in a CPAP humidifier.
Protecting CPAP Machine Function and Longevity
The primary mechanical issue caused by tap water is the accumulation of mineral deposits within the humidifier chamber. When the mineral-rich tap water is heated, the water evaporates, but the dissolved minerals do not. These minerals precipitate out and solidify, forming a hard, crusty residue known as limescale.
This mineral buildup coats the surfaces of the water tank and the heating element, degrading the machine’s performance. Over time, this scale acts as an insulator, reducing the efficiency of the heating element and making it difficult to maintain the necessary humidity level. Excessive scaling necessitates more frequent cleaning and shortens the operational lifespan of the equipment.
Reducing Health and Respiratory Risks
Beyond damaging the equipment, using tap water introduces potential health hazards, particularly within the respiratory system. The trace minerals left behind by evaporating tap water can be aerosolized, creating a fine white dust that is carried into the mask and inhaled directly into the lungs. Inhaling these microscopic mineral particles can cause irritation and inflammation in the airways.
Tap water is not sterile and may contain trace amounts of microorganisms, such as bacteria like Legionella or Pseudomonas, or mold spores. The warm, moist environment of the CPAP humidifier chamber provides an ideal breeding ground for these pathogens and for the formation of biofilms. When the water is converted into vapor, these contaminants can be inhaled, increasing the risk of respiratory infection.
What to Do When Distilled Water is Unavailable
While distilled water is the only recommended long-term solution, temporary alternatives exist for travelers or in a short-term pinch. Purified bottled water, filtered through processes like reverse osmosis, is a better temporary option than standard tap water. However, purified water may still contain trace minerals, so it should not be used regularly.
Boiling tap water for five minutes and allowing it to cool can kill most biological contaminants. It is important to remember that boiling water does not remove minerals, meaning the risk of mineral buildup and subsequent machine damage remains. If any alternative water source is used, the humidifier chamber should be thoroughly cleaned upon returning to a supply of distilled water.