CPAP therapy is a standard treatment for obstructive sleep apnea, delivering pressurized air through a mask to keep the airway open during sleep. Many CPAP machines include a heated humidifier to improve comfort and adherence to therapy. This reservoir adds moisture to the pressurized air, preventing nasal dryness and irritation. The water used must be distilled water, which is purified of nearly all minerals and contaminants, but its purity does not prevent contamination once introduced into the machine.
How Long Bottled Distilled Water Remains Usable
Unopened commercial bottles of distilled water generally maintain their quality for an extended period if stored correctly. The water itself does not spoil because it lacks the organic nutrients that support microbial growth. However, the packaging can degrade over time. Most manufacturers apply a “best by” date, often listing a shelf life of one to five years, which primarily relates to the integrity of the plastic container.
To maximize the shelf life, the sealed container should be stored in a cool, dark location away from direct sunlight. Sunlight can accelerate the breakdown of plastic and potentially leach compounds into the water. Once the seal is broken, the distilled water is exposed to the air, making it susceptible to contamination from airborne microbes and dust. For CPAP use, an opened container of distilled water should be used within a few weeks to ensure purity is maintained before it is poured into the reservoir.
How Often to Change Water in the CPAP Reservoir
The most important consideration for CPAP users is how long the water remains safe inside the machine’s reservoir. Manufacturers and health experts recommend changing the water in the humidifier chamber every day. This daily change is advised even with distilled water because the water is heated during use. This creates a warm, moist environment ideal for the growth of bacteria, mold, and algae.
Even if a small amount of distilled water remains after a night of use, it should be discarded rather than topped off. Exhaled air can introduce microbes into the water chamber, and standing water quickly develops a biofilm, which is a sticky layer of microorganisms.
To prevent microbial growth, residual water must be dumped each morning. The reservoir should be left open to air-dry completely during the day. Failure to empty and dry the chamber allows contaminants to multiply, increasing the risk of inhaling harmful substances and causing respiratory or sinus infections.
Preventing Contamination and Mineral Damage with Distilled Water
The strict recommendation for using only distilled water stems from two primary concerns: equipment damage and user health. Tap water, purified water, or spring water contain various levels of minerals, such as calcium and magnesium. These minerals are left behind as the water evaporates during heating. Over time, these deposits, known as scaling or limescale, accumulate on the heated plate and the humidifier chamber walls, compromising the machine’s performance.
This mineral buildup can reduce the efficiency of the humidifier, potentially leading to the failure of the heating element and may even void the CPAP machine’s warranty. Non-distilled water sources may also contain chemical additives, like chlorine or fluoride, and a higher concentration of microbes. Inhaling air that has passed over water containing these contaminants increases the risk of respiratory irritation and infection.