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Updated March 3, 2025
You’ve probably been there: it’s late, you’re getting ready to go to bed, and realize that your CPAP machine is out of water … and the bottle of distilled water that you usually use is empty too. But can you use purified water in your CPAP machine or even tap water as an alternative?
Not so fast - purified water and distilled or sterilized water are not the same, and medical experts strongly recommend that only sterile water be used in a CPAP machine. The occasional use of purified water in your CPAP machine is unlikely to cause harm to you or your machine, but you should clean the machine more frequently and refill it with distilled water as soon as you’re able.
It’s best to use distilled water in your CPAP because it’s completely free of all impurities, including bacteria, viruses, chemicals, and minerals. Distilled water is, technically, a type of purified water, but not all purified water is distilled. Depending on how the water is purified, it may still contain some contaminants, and even a small number of microorganisms. Purified water is typically very safe to drink, but inhaling it through your CPAP machine bypasses many of your body’s protective systems and can – in rare cases – cause illness.
It depends. It’s important to make the distinction between distilled, purified, filtered, and typical bottled water when considering CPAP water, because each has a slightly different definition.
Manufacturers and other sleep medicine experts typically do not recommend using tap water for a CPAP machine. Not all tap water is treated in the same way, and the safety of private drinking water wells is largely dependent on how they’re maintained. Although both water sources are usually clean and safe to drink, there have been cases in which individuals using CPAP machine water drawn from a private well developed respiratory illness linked to that water source.
Tap water and many purified waters also contain minerals, which can shorten the lifespan of your machine. If you use purified water in a CPAP machine rather than distilled, you should clean your CPAP machine more frequently – particularly if you see calcium deposits or other indications of mineral buildup. Follow your CPAP manufacturer's instructions for the best way to clean your machine.
Also note that mineral buildup in your water chamber can encourage bacteria growth and increase the risk of respiratory infections and persistent cold-like symptoms. If you notice buildup, it may be time to order a new CPAP water chamber. Check out our suggested CPAP replacement schedule to help ensure consistent, effective therapy.
Ultimately, the best water for a sleep apnea machine – whether it’s CPAP, BiPAP, or APAP – is sterile, distilled water. Unfortunately, many people don’t understand the difference between distilled water, purified water, bottled water, and tap water. A 2023 article in the journal Emerging Infectious Diseases reported that 42% of people surveyed believed they could use tap water for respiratory devices, such as CPAP machines. For your health – and the health of your CPAP machine – stick to distilled water in your humidifier.
