CPAP therapy treats sleep apnea and often uses a heated humidifier to add moisture to the pressurized air. This humidification greatly improves comfort by preventing dryness in the nose and throat. Since the water used in this chamber is exposed directly to the respiratory system, its purity is a significant concern for both machine maintenance and user health. Many people wonder if filtered water, such as Reverse Osmosis (RO) water, is an acceptable substitute for the universally recommended distilled water.
Why Water Purity is Critical for CPAP Humidifiers
The heated humidifier saturates the airflow with moisture by evaporating water. All water, even drinking water, contains Total Dissolved Solids (TDS), such as inorganic salts and organic matter like calcium and magnesium. When the water in the CPAP chamber is heated, only the pure water molecules (H₂O) evaporate. Non-evaporating impurities, including minerals and solids, are left behind in the reservoir. With each night of use, this process concentrates the remaining solids, leading to a rapid increase in the TDS level within the chamber.
Reverse Osmosis Water Versus Distilled Water
The difference between Reverse Osmosis (RO) and distilled water lies in their purification processes and resulting purity. Distilled water is produced by boiling water into steam and then condensing it back into liquid form. This process leaves behind virtually all minerals, salts, and microorganisms, resulting in water with TDS levels often as low as 2 ppm. RO water is filtered by forcing water under pressure through a semipermeable membrane. This process is highly effective, typically eliminating 90% to 99.5% of impurities. However, RO water is not sterile and may still contain trace levels of minerals or biological contaminants that the membrane did not fully block, meaning it is not as completely mineral-free or sterile as distilled water.
Practical Consequences of Using Non-Ideal Water Sources
Equipment Damage
Using water with high TDS leads to equipment damage. The concentrated minerals left behind in the humidifier chamber form a hard, crusty residue known as scale. This scale buildup coats the heating element and reservoir walls, reducing the humidifier’s efficiency. Over time, this residue can potentially cause the corrosion of internal components.
Health Risks
Non-sterile water also poses health risks by harboring microorganisms. The warm, moist environment of the humidifier chamber is an ideal breeding ground for bacteria and mold. Inhaling aerosols contaminated with pathogens like Pseudomonas or Legionella introduces these microbes directly into the respiratory tract, potentially leading to serious respiratory infections. Furthermore, mineral particles from the scale can become airborne and be inhaled, causing irritation to the airways.
Official Recommendations and Best Practices
CPAP machine manufacturers universally recommend using only distilled water in the humidifier chamber. This guarantees the lowest possible mineral content, protecting the machine from scale buildup and preserving the manufacturer’s warranty. Using any other water type, including RO water, introduces a risk of mineral accumulation and microbial growth that distilled water is designed to eliminate. If distilled water is temporarily unavailable, purified bottled water or filtered water are considered better short-term alternatives than tap water. This should only be an occasional measure. To mitigate risks when using non-distilled water, empty the water chamber every morning and clean it thoroughly with mild soap and water daily, in addition to a weekly deep cleaning.