CPAP Machines – How Much Water Do They Use And Why?


The water chamber in a CPAP machine typically holds around 11-17oz of water. As you sleep, this water is used to increase the humidity in the air you breathe in, which helps to make breathing (and sleeping) much easier. Knowing what causes CPAP machines to use more or less water will not only help you sleep better at night but is important, so the water lasts the whole night.

The amount of water used in the CPAP machine’s humidifier varies on the atmospheric humidity and your CPAP humidity level settings. More water is used during cold and dry weather (less than 40% humidity) or when you increase the temperature setting on your CPAP.

Monitoring the amount of water in the humidifier is the first step to ensure the machine’s smooth operation. Before this, you need to understand how a humidifier functions and why a CPAP machine needs a humidifier in the first place. Keep reading to find out more!

Why Does A CPAP Need Water?

Continuous Positive Airway Pressure (CPAP) therapy is a great way to treat sleep apnea and other respiratory illnesses. This procedure ensures a constant flow of air into the respiratory pathway and humidity plays an important role in this process.

A CPAP machine pulls air from the environment and directs it into the mask at a constant pressure. This in turn enters your nostrils and mouth at high pressure. During this process, the air in the mask can get dry and cold – especially in the winter months – and cause dryness and chapped lips. It can also lead to a dry mouth, a burning sensation in the nasal passage, and other complications.

When your nose becomes too dry and congested, some people find they tend to breathe more through their mouth. Mouth breathing worsens apnea and causes snoring too.

In fact, lowered humidity in the CPAP chamber can also cause sneezing and a runny nose. This is because as the nasal passage gets drier, the vascular tissue in the nostril secretes mucus as a lubricating mechanism. This causes sneezing and a runny nose. A humidifier in the room often does not make a noticeable difference.

Luckily most CPAP machines now come with an integrated humidifier or can be easily fit with a separate and detachable humidifier. The humidifier makes breathing and sleeping much easier and can help prevent nasal congestion, sneezing, and other side effects.

A CPAP humidifier infuses the pressurized air with adequate moisture before you breathe it in. The extent to which you should use the humidifier depends on the humidity in your room. If you use a CPAP machine it’s always a good idea to monitor the level of moisture in the area you usually sleep.

The EPA recommends you should keep humidity levels between 30 and 50%. For CPAP users, it is recommended to use the CPAP humidifier when humidity levels are anywhere below 40% – especially in the drier winter months. However, it’s important to get the humidity balance right as too much moisture can cause bacterial growth, allergies, and respiratory illnesses.

A hygrometer (humidity sensor) is used to monitor the humidity levels in your home and are great for bedrooms. A good humidity sensor will continually monitor the room and you can adjust how much you use your CPAP machine’s humidifier accordingly.

I’d recommend the Govee hydrometer. It has a large and easy-to-read display and can be set to alert your phone when the humidity goes out of your selected range, and it’s conveniently available on Amazon. Perfect! You can see their current prices by clicking here.

What Does A CPAP Machine Do?

In short, a CPAP humidifier makes breathing comfortable and easier while undergoing CPAP therapy.

To understand how this happens it’s important to first understand the mechanism of sleep apnea. Sleep apnea is a sleep disorder where breathing may slow down, become irregular, and suddenly stop several times during the night. This interruption can not only hinder sleep but also cause serious oxygen deprivation. If left untreated, this can cause strokes, heart attacks, high blood pressure, and headaches.

Sleep apnea is commonly associated with excess weight and obesity. While progressing through the sleep cycle, the throat muscles and tongue become relaxed and loose. At this point, excess soft tissue can weigh down on the upper respiratory tract and cause obstructions. This causes snoring and sleep apnea.

According to the National Center for Biotechnology Information, CPAP therapy prevents this irregularity by supplying constant air at a predetermined pressure through a mask. While asleep, this pressure ensures that breathing is regular. The CPAP machine consists of the main pressure body and a mask. This machine delivers the appropriate amount of pressure to keep your air passage open. This helps prevent sleep apnea and eliminates or reduces snoring. 

In addition to the mask, most CPAP machines today also have a humidifier to maintain optimal moisture conditions in the breathing environment.

How Often Should You Change The Water In A CPAP Machine

Just like any regular humidifier, you must empty the water from the CPAP humidifier tank every day even if there is some water remaining. Rinse the tank and refill it with fresh water. This is to prevent the growth of microorganisms. Rinse your tank under running water every day and pat dry with a towel before filling it up again.

In addition, wipe your tank down and clean it with dishwashing liquid or 2% vinegar solution once a week. Soak the chamber in the solution for 20 minutes, then wash and air dry. This is to ensure that your tank remains clean and sterile. After this, wash the tank two-four times with water until all traces of the chemicals have been removed.

Do not use tap water for this. Tap water is often hard; it contains dissolved minerals and impurities which can cause a scale buildup and even damage your CPAP machine over time. Similarly, do not use well water or spring water as this water is not demineralized – it contains dissolved calcium, magnesium, and other minerals.

For your CPAP humidifier, you need to use the purest water – always opt for distilled water. Distilled water is free from contaminants and does not cause any scale buildup. Distilled water can be purchased at your nearby convenience store, but it often ends up being cheaper to make it yourself using a home water distiller.

My #1 pick is the Megahome distiller (available on Amazon). It has a glass collector and a stainless-steel body making it very easy to keep hygienically clean – perfect for use with your CPAP!

Importantly, make sure you don’t overfill the water chamber. The humidifier tank has a maximum water level. Filling too much water can cause your device to cause a gurgling noise – like a boiling pot.

Where Does The Water Go In A CPAP Machine?

The humidifier in a CPAP machine has a special water reservoir (or chamber). The humidifier heats this water every time it is turned on. The CPAP machine passes the compressed air through this water tank so that moisture is picked up. After this, the humid air is pumped through a long tube into the CPAP mask.

How Often Should You Replace A CPAP Water Chamber?

Most manufacturers recommend changing the CPAP water tank every six months. Watch out for signs of degradation such as:

  • Pitted areas;
  • Cracks; or
  • Discoloration.

If you can see scale buildup and you can’t get it clean, it best to replace the water chamber. Keep in mind that cracked, dirty tanks can be a breeding ground for bacteria, which you don’t want to be breathing in at night. This can cause allergies and diseases.

Adjusting Moisture Levels In A CPAP Machine

Depending on atmospheric moisture levels in your room, you can adjust the heat level of your CPAP humidifier. Excess heat can lead to ‘rain’ inside your mask, where water condenses near the rims of the mask. This can interfere with your sleep cycle, by causing you to wake up with a wet mask slowly slipping off your face. To prevent this, turn down the heat a little and reduce the moisture output.

Keep in mind that your CPAP hose can also form ‘rain out’ condensation droplets – as the warm air flows to the mask from the device, it can condense within the tube and fall back to the tank. This can also make breathing uncomfortable. To prevent this, you can opt for a tube cover or heated tube.

Depending on the weather and the temperature of the humidifier, the heat setting can also be adjusted to prevent rain out inside the tube.

If the heat setting is too low, it can cause dryness and sneezing. In this case, turn up the heat a little.

Can I Use A CPAP Machine Without Water?

Yes, you can use your CPAP machine without water. Your machine will function normally but will obviously not provide added humidification.

However, it is important to care for your humidifier while not in use. An improperly stored water chamber can be a breeding ground for bacteria, spores, and mold. This can cause allergies. While not in use, keep your tank dry and sealed. Before using it again, wash it with a warm soapy solution and air dry. This keeps your equipment sterile and clean.

The Bottom Line

While a CPAP machine is one of the most recommended ways to treat sleep apnea, it is advisable to set up the required humidity levels in your room so that your sleep is uninterrupted. Choose the right type of water (distilled), don’t overfill your water chamber, and invest in a good CPAP humidifier so you can get the best night sleep possible. Sleep tight! 

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