A Continuous Positive Airway Pressure (CPAP) machine uses pressurized air to keep a patient’s airways open during sleep, primarily treating obstructive sleep apnea. The machine often includes a heated humidifier to add moisture to the pressurized air, preventing dryness in the nasal passages and throat. The quality of the water used in this humidifier is important for both the longevity of the equipment and the health of the user. While the question of using deionized (DI) water in a CPAP humidifier is common, manufacturers consistently recommend using only distilled water.
The Crucial Difference Between Deionized and Distilled Water
Many people mistakenly believe that deionized water and distilled water are interchangeable because both are highly purified forms of water. The difference lies in the purification method and the specific contaminants each process removes. Distillation is a thermal process where water is boiled into steam, which is then condensed back into a liquid state, leaving behind non-volatile impurities. This process effectively removes minerals, salts, heavy metals, and nearly all non-ionic contaminants like bacteria, viruses, and organic compounds.
Deionization, in contrast, is a chemical process that relies on ion-exchange resins to remove dissolved mineral ions, such as calcium, magnesium, and sodium. While deionized water is exceptionally free of ions, it does not remove non-ionic substances like bacteria, viruses, or volatile organic compounds (VOCs) because these contaminants do not carry an electrical charge. Therefore, DI water is chemically pure in terms of its mineral content, but it may be biologically less pure than distilled water.
Assessing the Risk of Using Deionized Water
Using deionized water in a CPAP humidifier introduces specific risks related to its extreme lack of ions. Water that is entirely free of ions is often described as “hungry” because it aggressively seeks to dissolve ions from any surrounding material to achieve electrochemical balance. This property means that deionized water can become mildly corrosive, potentially leaching trace amounts of metals or other materials from the plastic and metal components of the humidifier chamber and heating plate over time.
The leached compounds are then aerosolized and inhaled during therapy. Furthermore, because deionization does not eliminate non-ionic contaminants, the DI water may still harbor bacteria, viruses, or organic molecules that could be aerosolized and breathed into the lungs. This potential inhalation of microbes or trace chemicals is a significant health concern. CPAP manufacturers specifically advise against using DI water to avoid these risks, which compromise both the machine’s integrity and the user’s health.
Why Distilled Water is the Only Recommended Option
Distilled water is the standard recommended by CPAP manufacturers because its dual purification process ensures the removal of both mineral and biological contaminants. The distillation method yields water that is virtually free of minerals, preventing the buildup of scale or residue inside the humidifier chamber. This mineral-free quality protects the machine’s heating element and maintains its long-term performance.
Distilled water also safeguards the user’s health by eliminating microbes and other non-ionic impurities that could be aerosolized and inhaled. Tap water, while safe to drink, contains varying levels of minerals like calcium and magnesium, which condense on the heating plate as white, crusty deposits, reducing the efficiency of the humidifier. The use of tap water also introduces the risk of inhaling chlorine, fluoride, or other chemical additives, as well as potential pathogens, which can lead to respiratory irritation or infection. Purchasing readily available distilled water is the only acceptable practice to ensure safety and proper CPAP operation.