Continuous Positive Airway Pressure (CPAP) therapy uses a machine to deliver pressurized air through a mask, which helps keep the user’s airway open during sleep. Many CPAP devices include a heated humidifier, which adds moisture to the airflow to prevent common side effects such as dry mouth, throat irritation, and nasal congestion. The water used in this humidifier chamber evaporates into the air the user breathes, making the selection of water type a significant consideration for both long-term machine functionality and the user’s respiratory health. Since the air passes directly into the lungs, the quality of the water must be controlled to avoid introducing contaminants or mineral deposits into the system.
Why Distilled Water is the Standard
Distilled water is the universal recommendation from CPAP manufacturers because it contains virtually no dissolved solids, minerals, or contaminants. This near-total purity is achieved through the process of distillation, which involves boiling the water and then collecting the resulting steam as it condenses back into liquid. By turning the water into vapor, this method effectively leaves behind almost all inorganic compounds, salts, and microbes. The resulting water is considered the cleanest available for medical devices because it has a Total Dissolved Solids (TDS) measurement of zero or near-zero. This zero-mineral content is crucial for preventing the formation of scale, the hard, crusty residue left behind when mineral-rich water evaporates.
The Acceptability of Purified Water
The question of whether purified water is a suitable alternative is complex because “purified” is a broad term that describes any water that has undergone a treatment process to remove chemicals and contaminants. This purification often utilizes methods like deionization, carbon filtration, or reverse osmosis (RO). Purified water is entirely safe for drinking, but its mineral content, while very low, is not always zero.
Trace amounts of minerals may remain in purified water, which can lead to slight residue buildup over time compared to the complete removal achieved by distillation. For this reason, while experts agree that distilled water is the optimal choice, purified water can be an acceptable substitute for short-term or emergency use. If you must use purified water, it is advisable to choose a brand that explicitly states it has not been remineralized. Long-term use of purified water may still require more frequent cleaning of the humidifier chamber than would be necessary with distilled water.
Risks of Using Tap Water
Using tap water in a CPAP machine’s humidifier poses two significant risks: damage to the equipment and potential health concerns. Tap water contains naturally occurring minerals, such as calcium and magnesium, which contribute to its hardness. When the CPAP humidifier heats this water, the water evaporates, but these non-volatile minerals are left behind. These leftover minerals crystallize and form scale deposits on the heating plate and the walls of the water chamber.
This mineral buildup can reduce the humidifier’s ability to heat the water effectively, leading to a decrease in the humidification delivered and potentially shortening the machine’s overall lifespan. Excessive scale can also make the chamber difficult to clean and may even void the manufacturer’s warranty. Tap water can also harbor microorganisms. Since the CPAP machine aerosolizes the water, these pathogens bypass the body’s natural defenses and are inhaled deep into the lungs. Inhaling these contaminants can lead to respiratory irritation or serious infections.