A CPAP machine uses a heated humidifier to add moisture to pressurized air, which prevents dryness and makes therapy more comfortable. The quality of the water used is a critical consideration, impacting both the device’s longevity and the user’s respiratory health. While deionized water is extremely pure, CPAP manufacturers universally recommend distilled water as the standard choice for safe and effective use. This distinction is rooted in how each type of water is processed and the specific impurities they remove.
The Recommended Standard for CPAP Humidifiers
The established recommendation for all CPAP humidifiers is the use of distilled water. Distillation is a purification method that involves boiling water and then collecting the steam as it condenses back into liquid form. This physical separation process effectively leaves behind almost all Total Dissolved Solids (TDS), including minerals, salts, and other inorganic compounds.
Water free of these inorganic compounds prevents the formation of scale, or mineral buildup, within the CPAP’s water chamber and on the heating plate. Scale formation reduces the efficiency of the humidifier and requires frequent, difficult cleaning. By preventing this residue, distilled water helps ensure the machine maintains its intended performance and significantly extends the operational lifespan of the humidifier component.
Deionized Water Versus Distilled Water
Deionized (DI) water and distilled water are both highly purified, but they achieve purity through fundamentally different methods. Deionization relies on an ion-exchange process, passing water through electrically charged resins that attract and remove charged mineral ions like calcium, magnesium, and sodium. This process is designed solely to remove ions.
The primary concern with using deionized water is its potential to harbor non-ionic contaminants. Unlike distillation, deionization does not reliably remove uncharged substances such as bacteria, microorganisms, and volatile organic compounds. These impurities could still be aerosolized by the CPAP humidifier and inhaled, posing a health risk to the user.
Furthermore, extremely pure water, sometimes called “hungry water,” is chemically reactive and may attempt to leach ions from the materials it contacts, including the CPAP reservoir’s plastics and metals. Manufacturers avoid recommending DI water because distilled water offers a broader removal of all contaminant types, including biological ones, making it the safer choice for medical equipment. The manufacturer’s warranty often specifies the use of distilled water, making it the definitive standard.
Risks of Using Tap Water
Using ordinary tap water in a CPAP machine’s humidifier carries two distinct negative consequences: one for the device and one for the user’s health. Tap water contains varying levels of minerals, most commonly calcium and magnesium, which are known as Total Dissolved Solids.
When the water is heated and converted to vapor, these minerals are left behind in the water chamber. This mineral residue quickly forms a crusty, white scale on the heating element and the inner surfaces of the reservoir. This scale reduces the heating plate’s ability to warm the water efficiently and necessitates frequent, aggressive cleaning that can damage the chamber.
Beyond the mechanical issues, tap water may also contain trace amounts of pathogens like Legionella and Pseudomonas bacteria. When the humidifier converts the water into a fine mist, these microorganisms can become aerosolized and directly inhaled into the lungs, potentially leading to respiratory infections.