The standard recommendation for a Continuous Positive Airway Pressure (CPAP) machine humidifier is to use distilled water exclusively. Distilled water is pure H₂O, devoid of the minerals and microorganisms found in most tap water supplies. While using tap water for a single night is not ideal, most healthy individuals can generally tolerate this temporary measure, though it is not without risk. Immediate and thorough cleaning is required afterward to mitigate the resulting biological and mechanical issues. The primary concerns are inhaling airborne pathogens and the formation of mineral scale that can degrade the equipment.
Immediate Biological Risk of Tap Water
Tap water, classified as unsterile by the Centers for Disease Control and Prevention (CDC), contains various microorganisms. These are typically harmless when swallowed because stomach acid eliminates them. However, a CPAP humidifier heats the water and converts it into a fine aerosol mist. This mist is inhaled directly into the respiratory system, bypassing the body’s natural defenses in the lungs.
Inhaling aerosolized pathogens can lead to severe respiratory infections, especially for users with existing conditions like COPD or compromised immune systems. Pathogens such as Legionella species and Pseudomonas aeruginosa thrive in the warm, moist environment of a CPAP water chamber. Documented cases of life-threatening pneumonia are linked to using unsterile water in CPAP equipment. The warmth and moisture create a breeding ground, allowing contaminants from tap water to rapidly colonize internal surfaces.
Equipment Damage From Mineral Deposits
Tap water contains varying concentrations of dissolved minerals, primarily calcium and magnesium, which contribute to water hardness. When the CPAP humidifier heats the water, the pure water evaporates, leaving these non-volatile mineral solids behind in the water chamber and on the heating plate. This residual buildup is known as scale or limescale.
This crusty residue reduces the humidifier’s efficiency, requiring the machine to work harder to achieve the desired humidity level. The scale can obstruct air passages and interfere with the heating element’s ability to transfer heat effectively. Even a single night of use, especially with very hard water, can leave behind a visible, chalky residue. These mineral deposits also create microscopic crevices that harbor bacteria and fungi, making the chamber difficult to keep hygienic and clean.
Post-Use Cleaning and Mitigation Steps
After using tap water for one night, immediate and thorough cleaning is necessary to mitigate mineral and microbial risks. First, completely empty the water chamber of any remaining tap water right away; do not leave standing water in the reservoir. The chamber should then be disassembled, if possible, and washed with a mild, unscented dish soap and warm water.
To address nascent mineral scale, soak the chamber in a solution of one part white vinegar to three or four parts distilled water for about 30 minutes. Vinegar is a mild acid that effectively dissolves calcium and magnesium deposits without damaging the plastic components of the device. After soaking, rinse the chamber thoroughly with distilled water several times to remove residual mineral particles and the vinegar smell. The water chamber must then be allowed to air dry completely before being reassembled, as residual moisture encourages microbial growth.