What type of water for your CPAP humidifier? Why you don’t need to use expensive speciality water

“Do I really need to use expensive speciality water?” This is one of the most frequent questions from our customers about CPAP humidifiers. The good news: No, you don’t. Find out why not here.

The differences in the official manufacturer recommendations are remarkable

Firstly, manufacturers of leading CPAP devices disagree about what type of water should be used for their CPAP humidifiers. A comparison of the usage instructions from Löwenstein, ResMed and Philips clearly shows some of these differences:

Instructions for use: Löwenstein prismaAQUA, ResMed Humidair, Philips Respironics Dreamstation Humid, Heated Tube Humidifier

Judging by this table, it’s no surprise that customers have questions. So who’s right? Well, the crucial thing here is the water quality. 

Quality from the tap: Why British drinking water is perfectly adequate.

Tap water in the UK has a low level of bacteria and harmful substances (though regional variations exist), so the prevailing opinion is that normal UK tap water can be used to fill CPAP humidifiers without any concerns. The tap water isn’t completely free from bacteria or harmful substances, but the limit values are strictly regulated by the Drinking Water Inspectorate (DWI) to ensure the levels are harmless. And it gets even better: the way the humidifier works actually increases the safety of the water.

How so? Well, in CPAP humidifiers, air flows via the surface of the water, and the humidifiers only pick up water molecules (in the form of steam). The key thing here is that this steam does not contain any substances that are dissolved in the water, or any bacteria or germs.

This has been verified in various studies, including one involving radio-labelled filling water; even after hours of operation, no radio-labelled substances were detected in the humidified air of a respiratory therapy device. Steam simply does not pick up any substances from the water. 

Boiling the tap water: extra protection?

Let’s say that someone has particular pre-existing conditions, e.g. serious respiratory diseases: would boiling the tap water provide any additional safety, or could it even be harmful? After all, it’s a well-known fact that boiling tap water significantly reduces the amount of germs. 

There is, however, an argument that this would leave heat-resistant residues of fungi and bacteria that cannot be rendered harmless just by boiling the water once. According to this argument, the water should be heated and allowed to cool several times over a period of 3 days. However, the kind of resistant spore that requires this type of interval-boiling is generally very rare in drinking water. This applies not only to drinking water in UK, but also in other industrialised countries such as the USA. The recognised US government health institution the CDC is clear in its assessment: To sterilise water for use in humidifiers, it is sufficient to boil the water for five minutes and then leave to cool.

The key difference: what you need to know about “distilled” water

What’s the situation with distilled water? Can it be used with confidence? When answering this question, it’s important to distinguish between demineralised water and “real” distilled water.  

The “distilled” water commonly found in retail trade is actually demineralised water, where only the minerals and salts have been removed from the water. This is important when the water is being used for car batteries or as ironing water, for example (Löwenstein refers to this as “distilled water for technical purposes”). For these purposes, however, it doesn’t matter whether the water is completely free from germs, i.e. that it doesn’t contain any bacteria, viruses or fungi, so this is also not guaranteed by the manufacturers (for reasons of product liability). 

We do not recommend using this type of water for respiratory humidifiers; after all, you can achieve the same level of safety with normal tap water as long as you carry out regular maintenance and care of your humidifier.

Sterile water: maximum safety (and right when you need it)

“Real” distilled water, on the other hand, is indeed free from germs as it contains water molecules and nothing else. Crucially, this remains the case after filling, and this is guaranteed by manufacturers. This is referred to as “sterile” water. 

These products are regularly used in the medical field, particularly for rinsing solutions for wound care, in which case they are classed as medical devices (identifiable by the CE mark with number, the stamp with the word STERILE and the MD symbol for “medical device”). Due to the stringent requirements, this type of water is very expensive with only limited market availability. In our view, the use of sterile water for respiratory ventilation is only necessary in exceptional medical cases (usually on the explicit instruction of the handling physician). 

Important care tips: keeping your CPAP humidifier perfectly hygienic

The right care, on the other hand, is crucial to the hygiene of your CPAP humidifier, namely daily water changes and regular cleaning: 

• The humidifier water must be fully replaced every day. Standing water can quickly become a breeding ground for germs and fungi – even if it started off completely clear. Replacing the water every day is therefore a simple yet effective preventive measure.
• It’s just as important to regularly clean the humidifier, e.g. using SomnoSept, and to descale the heating plate. This not only prevents hygiene problems, but also keeps your device fully functional.

Sources: 

Oto J, Imanaka H, Nishimura M. Clinical factors affecting inspired gas humidification and oral dryness during noninvasive ventilation. J Crit Care. 2011; 26:535.e9-535.e15. https://doi.org/10.1016/j.jcrc.2010.10.005

Miko S, Colier S, Burns-Lynch C, (Mis)perception and Use of Unsterile Water in Home Medical Devices, PN View 360+ Survey, United States, August 2021, https://www.cdc.gov/drinking-water/prevention/preventing-waterborne-germs-at-home.html

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Dr. Daniel Grätz

Dr. Daniel Grätz is the Managing Director of health.On Ventures GmbH, one of Germany’s leading online providers of snoring mouth guards, and has been providing customers with advice about these devices for many years.