Continuous positive airway pressure (CPAP) therapy can provide significant relief for people with sleep apnea . Untreated sleep apnea can cause people to gasp, choke, or stop breathing while asleep.

CPAP machines deliver pressurized air to help sleepers’ breathing passages stay open. While this can significantly reduce sleep apnea symptoms, some users experience side effects such as dry mouth, sinus congestion, or other irritations.

Using a CPAP humidifier can help combat these issues. The humidifier uses water to keep breathing passages moist and comfortable. Some CPAP machine models have humidifiers incorporated within their designs, though not all do.

We’ll take an in-depth look at CPAP humidifier best practices and explain why distilled water is a better choice than other forms of water.

Benefits of Using a CPAP Humidifier

The continuous flow of air that comes from a CPAP machine can feel drying. Some CPAP users report irritation in their nose and throat, including nose bleeds, sinus congestion, and dry mouth. A CPAP humidifier adds water to the pressurized air to increase humidity and make breathing with a CPAP device more comfortable.

If you use a CPAP machine and routinely wake up with dry breathing passages, you may want to consider adding a humidifier to your CPAP setup. It is also critical to regularly clean your CPAP machine, including your mask and other device components.

Why You Should Use Distilled Water in a CPAP Machine

While tap water is readily accessible and may be tempting to use in your CPAP humidifier, it can contain mineral deposits and other chemicals that may damage your machine or result in potentially harmful bacterial growth . In terms of bottled water options, they can be boiled down to the following categories:

  • Purified water: Most bottled water is purified, meaning it is filtered to remove chemicals, though it may still contain some mineral content . Most purified drinking water sold in stores originates as municipal tap water. Some brands employ a reverse osmosis process, which removes impurities and microbes by using pressure to force water through a semipermeable membrane. Bottled water produced through these purification methods is often remineralized to provide healthy minerals for drinking.
  • Spring water: Generally rich in mineral content, spring water comes from aquifers and is naturally filtered underground before it reaches an above-ground spring. Artesian water is similar to spring water, but it comes from an artesian well that taps an aquifer.
  • Mineral water: Mineral water sold in the U.S. must come from an underground water source and needs to contain a minimum amount of total dissolved solids to be branded as such.
  • Distilled water: Considered the purest form of bottled water, distilled water is produced by boiling water and then condensing the vapor back into liquid form.

Distilled water is the best choice for CPAP humidifiers because it’s pure water that is free of minerals and bacteria. Hospitals, labs, and factories often use distilled water instead of tap water because it prevents limescale buildup on devices.

Using the wrong type of water in your CPAP humidifier can cause mineral buildup, scaling, or bacterial growth. It may also irritate your airways or cause your machine or its components to break down.

Is It Better to Buy Distilled Water Instead of Distilling It Yourself?

Though distilling water is fairly simple to do at home, it’s generally best to purchase distilled water for use in your CPAP humidifier. Labs and factories have quality control procedures that ensure each bottle of distilled water is processed correctly before it’s sold to consumers. When you distill water at home, you don’t have these safeguards.

Does Purified or Filtered Water Work as a Substitute for Distilled Water?

Purified or filtered water can contain minerals that may lead to buildup in your CPAP machine, so it’s best to use distilled water. The distilling process eliminates minerals, chemicals, and bacteria, leaving the purest possible water behind.

Best Place to Buy Distilled Water

Distilled water is easy to find. Most grocery stores, drug stores, and mini-markets carry distilled water. You can also buy it from online stores and CPAP suppliers. Some online retailers offer subscriptions so that you don’t have to worry about reordering or running out.

Why Tap Water Is Not a Substitute for Distilled Water in a CPAP Machine

Tap water can come from a well or a municipal water supply. Though your tap water may be perfectly fine to drink, it may contain minerals that can cause buildup or scaling in your CPAP machine. Tap water may also contain additives like chlorine or fluoride that can harm your machine.

While you can boil water to kill bacteria, it will still contain any mineral content that was there prior to boiling.

Frequently Asked Questions

Can you use spring water in a CPAP machine?

You should use distilled water instead of spring water in your CPAP humidifier. Spring water comes from natural underground water sources that reach the earth’s surface. This water may be naturally high in mineral content or contain other organic material. Spring water may be refreshing to drink, but when you run it through your humidifier the minerals can cause the machine’s components to break down.

Can you use reverse osmosis water in a CPAP machine?

Reverse osmosis refers to a purification process in which water is forced through a semipermeable membrane to remove sediment, bacteria, and chemicals. While it is generally more thorough than traditional filtration methods, water filtered via reverse osmosis still retains some dissolved solids , making it less suitable than distilled water for CPAP humidifiers.

Additionally, some at-home reverse osmosis systems are more effective at removing contaminants than others, and their effectiveness can degrade over time. Bottled water brands that use reverse osmosis often remineralize the water following the purification process.

Can you use bottled water in a CPAP machine?

You can use bottled water in your CPAP humidifier if it is distilled water. Most bottled water used for drinking is purified or spring water. These don’t contain bacteria, but they may have minerals like calcium and magnesium that can leave residue in your humidifier and may cause it to wear out quicker than expected. Use bottled distilled water for the best possible results.

Learn more about our Editorial Team

7 Sources

  1. Strohl, K. P. (2020, September). Sleep apnea. Merck Manual Consumer Version., Retrieved May 17, 2022, from
  2. Ghadiri, M., & Grunstein, R. R. (2020). Clinical side effects of continuous positive airway pressure in patients with obstructive sleep apnoea. Respirology, 25(6), 593–602.
  3. Raymond, L.W., Barkley, J.E., Langley, R., & Sautter, R. (2009). Prolonged respiratory illness after single overnight continuous positive airway pressure humidification: Endotoxin as the suspect. Southern Medical Journal, 102(12), 1260–1262.
  4. U.S. Environmental Protection Agency. (2005, September). Water health series: Bottled water basics., Retrieved May 17, 2022, from
  5. Centers for Disease Control and Prevention. (2020, August 4). A guide to drinking water treatment technologies for household use., Retrieved May 17, 2022, from
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  7. Abd El-Salam, M.H. (2003). Membrane techniques: Applications of reverse osmosis. Encyclopedia of Food Sciences and Nutrition, 3833–3837.

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