Continuous Positive Airway Pressure (CPAP) therapy is a common treatment for obstructive sleep apnea, delivering pressurized air through a mask to keep the user’s airway open during sleep. Many CPAP devices include a heated humidifier, which adds moisture to the air flow to prevent common side effects like nasal dryness, congestion, and throat irritation. The humidifier warms water, creating vapor that is carried into the mask along with the pressurized air. However, the type of water used is a major consideration, and most manufacturers advise against filling the reservoir with standard tap water.
How Tap Water Damages CPAP Equipment
The primary issue with untreated water is the presence of dissolved minerals (calcium, magnesium, and iron) responsible for water hardness. When the CPAP humidifier heats this water, the pure water turns into vapor, but non-water components are left behind in the reservoir.
This process concentrates the minerals, leading to the formation of a hard, chalky residue known as scale. Scale quickly deposits on the heating element and the walls of the humidifier chamber. The buildup of this film insulates the heating plate, significantly reducing its efficiency and requiring the machine to use more energy.
Over time, the constant mineral deposition can corrode internal components and rubber seals, shortening the operational lifespan of the CPAP humidifier. In some cases, using water containing high mineral content may even void the manufacturer’s warranty.
Respiratory Health Risks Associated with Tap Water Use
Beyond mechanical damage, unsterile water poses direct risks to respiratory health. Tap water, while safe for drinking, is not sterile and often contains low levels of microorganisms, including bacteria, fungi, and protozoa. The warm, stagnant environment of the humidifier tank acts as an incubator, allowing any present microbes to multiply rapidly.
Pathogens such as Pseudomonas aeruginosa and Legionella bacteria, as well as amoebas like Acanthamoeba, can thrive in this environment. When the CPAP machine converts the contaminated water into an aerosol, these microbes can be directly inhaled deep into the sinuses and lungs. The respiratory system is more vulnerable to inhaled contaminants than the digestive tract. Inhaling these aerosolized organisms can lead to respiratory infections, especially in individuals with underlying health conditions or compromised immune systems.
Tap water is also treated with chemicals like chlorine and fluoride to ensure it is potable. While these chemicals are harmless when swallowed, they become irritants when vaporized and channeled directly into the delicate tissues of the lungs and airways. Inhaling these volatile substances can cause irritation to the nasal passages and bronchial tubes. The risk profile shifts substantially when water is aerosolized and delivered under pressure compared to when it is swallowed.
Why Distilled Water is the Standard
Distilled water is the industry standard recommendation for CPAP humidifiers because it is processed to remove nearly all impurities. The distillation method involves boiling water into steam and then condensing the steam back into a liquid. This two-step process effectively separates the water molecules from minerals, chemicals, and most microbes, resulting in an exceptionally pure product.
This purity means that when distilled water is heated, virtually nothing is left behind, completely preventing the damaging scale buildup seen with tap water. The lack of minerals and microorganisms protects the user’s respiratory system from irritation and the risk of infection. Standard home water filters do not remove the dissolved minerals that cause scaling, meaning filtered water is not an adequate substitute.
Boiling tap water is a common emergency alternative, as it kills most harmful bacteria and other pathogens, addressing the microbial contamination risk. However, boiling does not remove any dissolved mineral solids; in fact, as some water evaporates during the process, it can slightly concentrate the remaining minerals. Therefore, using boiled and cooled tap water is a temporary solution that protects against infection but will still cause scaling and damage to the CPAP equipment over time.
Essential Humidifier Cleaning and Maintenance
Regardless of the water source, regular cleaning of the humidifier chamber remains an important practice to ensure a healthy and functional device. Daily maintenance should include emptying any remaining water from the reservoir immediately after use. This prevents the water from sitting and becoming a breeding ground for residual mold, bacteria, or other contaminants.
At least once a week, the humidifier chamber should be disassembled and washed thoroughly. A mild, non-fragranced dish soap and warm water are effective for this routine cleaning. For a deeper clean, a solution of one part white vinegar to three parts water can be used to soak the chamber for about 30 minutes. This soaking helps dissolve any minor mineral deposits or remove biofilm. After washing or soaking, the chamber must be rinsed completely with fresh water and allowed to air dry fully before being reassembled.