Continuous Positive Airway Pressure (CPAP) therapy is a widely used treatment for sleep apnea, delivering pressurized air through a mask to keep airways open during sleep. Many CPAP devices include a heated humidifier to add moisture to the airflow, which improves comfort by preventing dryness in the nose and throat. This humidification relies on the water placed into the reservoir, making its quality and management a frequent concern for users. A common question is whether the distilled water remaining in the humidifier chamber from a previous night can be safely reused.
The Immediate Answer to Reusing Water
The simple answer is that no, the water from a CPAP humidifier should never be reused for a subsequent night of therapy. Even if the water was freshly distilled when added and appears perfectly clear, it must be discarded immediately after each use. This strict protocol is necessary because the environment inside the CPAP reservoir quickly becomes a habitat for microbial growth.
The conditions for contamination are created when the water is warmed by the heating plate and then left stagnant after the machine is turned off. This warm, moist atmosphere allows bacteria, fungi, and molds to multiply rapidly, turning the remaining water into a contaminated liquid. Organisms like Pseudomonas or mold spores can begin to colonize the interior surfaces of the chamber.
When the machine is reactivated, the CPAP’s humidification process aerosolizes the water, turning the liquid into a fine mist delivered directly into your respiratory system. The delicate tissues of the lungs and airways lack the robust acid defenses found in the digestive tract, leaving them vulnerable to inhaled microbes. Reusing the water increases the risk of introducing these contaminants deep into the lungs, potentially leading to respiratory infections or irritation.
Why Distilled Water is Required
The requirement for distilled water is separate from concerns about microbial contamination and focuses on the mechanics and longevity of the CPAP device. Tap water, filtered water, and even bottled spring water contain dissolved minerals, primarily calcium and magnesium. While these minerals are harmless for drinking, they become problematic when heated and evaporated.
As the CPAP humidifier heats the water to create vapor, the pure water molecules turn into gas and leave the chamber, but non-volatile mineral solids are left behind. These residual minerals precipitate out of the water and form a hard, crusty residue known as limescale or scaling on the heating plate and the interior of the water chamber. This buildup accumulates over time.
The presence of limescale reduces the efficiency of the humidifier by insulating the heating element, forcing the machine to work harder to achieve the desired humidity level. This can lead to inconsistent humidification and damage to the machine’s components. Using anything other than distilled water can cause premature failure of the water tank and may void the manufacturer’s warranty.
Daily and Weekly Reservoir Care
Proper maintenance of the water reservoir requires daily attention and a more thorough weekly cleaning to ensure hygiene and performance. The daily protocol begins upon waking, when any water remaining in the chamber must be poured out completely. The chamber should then be rinsed with clean water to remove any loose particles or residue.
The most important step in the daily routine is allowing the reservoir to air dry thoroughly during the day. Keeping the chamber lid open and placing it away from direct sunlight prevents residual moisture from creating a damp environment where pathogens can thrive. A completely dry surface inhibits the growth of mold and bacteria before the chamber is refilled with fresh distilled water.
For a more comprehensive cleaning, the water chamber should be washed weekly using warm water and a mild, unscented dish soap. Strong, scented, or antibacterial soaps should be avoided because their chemical residues can leave behind fumes that may be irritating or harmful when inhaled. Once washed, the reservoir must be rinsed meticulously with clean water to remove all soap film.
Periodically, a deeper disinfection may be necessary, which can be accomplished using a mild vinegar solution. A common recommendation is to soak the chamber for 20 to 30 minutes in a mixture of one part white distilled vinegar to four parts water. Following this soak, the chamber must be rinsed extensively with clean water to eliminate any lingering vinegar odor, and then left to air dry. Manufacturers also recommend replacing the water chamber entirely, typically every six months to a year, because plastic components can degrade or develop micro-fissures that harbor germs.