A Continuous Positive Airway Pressure (CPAP) machine supports breathing for individuals with conditions like obstructive sleep apnea by delivering pressurized air through a mask to keep the airway open during sleep. Many CPAP units include an integrated humidifier, which warms and moistens the air before it reaches the user’s lungs. This feature significantly improves patient comfort, reducing dryness and irritation in the nasal passages and throat. The quality of the water used in the humidifier reservoir is a primary consideration for the machine’s performance and the user’s health.
Distilled Water vs. Reverse Osmosis Water
The fundamental difference between distilled water and reverse osmosis (RO) water lies in the purification method and the resulting concentration of Total Dissolved Solids (TDS). Distillation is a thermal process that involves boiling water into steam and then condensing the steam back into a liquid form. This process effectively leaves behind virtually all dissolved minerals and impurities, resulting in water with a TDS level close to zero.
Reverse osmosis is a filtration method that uses pressure to force water through a semi-permeable membrane. This membrane has microscopic pores that block most dissolved solids, contaminants, and large molecules. While RO systems are highly effective, removing up to 99.5 percent of impurities, they may not achieve the zero-TDS standard of true distilled water. Consequently, RO water can sometimes retain trace amounts of minerals or volatile organic compounds that passed through the membrane.
Manufacturer Guidelines for CPAP Humidifiers
CPAP machine manufacturers overwhelmingly recommend using only distilled water in the humidifier reservoir. This recommendation is based on the guaranteed, near-zero mineral content of distilled water, which is the most suitable for the heated environment. While RO water is a highly purified alternative and is significantly better than untreated tap water, it is not the standard recommendation for long-term use.
The primary concern with RO water is that the trace amount of minerals that may remain can still lead to gradual buildup inside the machine. Additionally, the RO process can sometimes result in water with a slightly lower pH level, making it more acidic than distilled water. Although this lower pH is rarely a human health concern, it can potentially affect the plastic or metallic components of the humidifier over a long period.
Most CPAP user manuals are explicit in their instruction to use distilled water exclusively to maintain the integrity and longevity of the equipment. Using a water source that is not fully demineralized, even purified water like RO, introduces a persistent risk of mineral deposition. Distilled water remains the universally endorsed choice among machine manufacturers and sleep specialists.
The Impact of Mineral Content on CPAP Longevity
The most significant consequence of using water that is not fully demineralized is the formation of scale and mineral buildup inside the humidifier chamber. When water containing minerals is heated, the pure water evaporates, but the dissolved solids are left behind. These solids precipitate, forming a hard, white, chalky residue known as scale on the heating plate and the walls of the water reservoir.
This mineral scale directly impacts the performance and lifespan of the CPAP unit. The buildup can obstruct air passages, reduce the efficiency of the heating element, and affect the accuracy of internal sensors that regulate temperature and humidity levels. Over time, this degradation can compromise the quality of the sleep therapy and necessitate more frequent cleaning to dissolve the deposits.
Relying on water other than the manufacturer-recommended distilled water can have financial implications for the user. The use of non-recommended water types is a known cause of premature wear and can sometimes void the warranty on the humidifier components. The resulting damage from scale buildup may require costly replacement of the water chamber or the entire machine.