Continuous Positive Airway Pressure (CPAP) therapy is a common and effective treatment for obstructive sleep apnea. The machine delivers a steady stream of pressurized air through a mask, preventing the airway from collapsing during sleep. Many CPAP devices include a heated humidifier to add moisture to the airflow, preventing dryness and irritation. Manufacturers consistently recommend using only distilled water in the reservoir to maintain equipment integrity and user safety.
Equipment Damage from Mineral Deposits
When water is heated and converted into vapor within the CPAP humidifier, only pure water molecules are aerosolized. Tap water and most bottled waters contain dissolved solids, primarily minerals like calcium and magnesium, which are components of “hard water.” These minerals do not evaporate and are left behind in the water chamber and on the heating plate.
As the heating process repeats nightly, the concentration of remaining minerals increases significantly. This causes the minerals to precipitate out, forming a hard, chalky residue called scale or limescale. This buildup adheres to the surfaces of the water tank and the heating element, reducing the humidifier’s efficiency.
Scale necessitates more frequent cleaning and, if unchecked, can lead to permanent damage. Mineral deposits can obstruct small components and cause the heating element to overheat or fail prematurely. Distilled water prevents this damaging accumulation because the process removes nearly all dissolved solids, preserving the lifespan of the CPAP equipment.
Introducing Health Risks from Contaminants
The most serious consequence of using non-distilled water relates to respiratory health. Tap water is safe for drinking because the digestive system neutralizes contaminants, but the respiratory system lacks this robust defense. The CPAP humidifier aerosolizes the water into a fine mist delivered directly into the user’s lungs.
Tap water is not sterile and often contains trace microorganisms, including bacteria like Pseudomonas aeruginosa and Legionella spp., which cause respiratory infections. It can also harbor free-living amoebae, such as Acanthamoeba. The warm, moist environment inside the CPAP water chamber creates an ideal breeding ground where these pathogens multiply rapidly, forming biofilms.
Once aerosolized, these biological contaminants are inhaled deep into the airways, potentially leading to respiratory illnesses ranging from irritation to severe pneumonia. This risk is elevated for individuals with underlying conditions or compromised immune systems. Tap water may also contain trace chemicals like chlorine or fluoride, which, when inhaled, can act as respiratory irritants. The direct inhalation route bypasses the body’s natural filtering mechanisms, making water purity paramount for safe therapy.
Temporary Solutions and Emergency Use
Distilled water may occasionally be unavailable, such as during travel or an unexpected shortage. In these emergency situations, a temporary alternative can be used, but it must be prepared carefully and should not become routine practice. The primary goal is to sterilize the water to eliminate immediate biological contaminants.
Tap water can be sterilized by boiling it vigorously for a full minute (or three minutes at higher altitudes). The water must be allowed to cool completely before being poured into the reservoir. Boiling kills most microbes, but it does not remove dissolved minerals.
This temporary solution addresses the microbial threat but does not prevent the long-term equipment damage caused by mineral buildup. Bottled spring water or purified water from a filter pitcher are not recommended alternatives, as they still contain minerals and may not be sterile. Any use of non-distilled water should be limited to one or two nights, followed by a thorough cleaning of the water chamber.