If you or a family member has recently been prescribed a CPAP machine, you may be wondering:
- What condition is it treating?
- Why does the machine need water?
- And what type of water should you be using?
CPAP therapy is most commonly prescribed for sleep-related breathing disorders — and when a humidifier is used, water quality becomes extremely important.
Using the correct distilled water helps protect your machine, reduce limescale build-up, and maintain hygiene during long-term use.
👉 View distilled water suitable for CPAP machines here
The Most Common Reason: Obstructive Sleep Apnoea (OSA)
The most common reason a CPAP machine is prescribed in the UK is Obstructive Sleep Apnoea (OSA).
OSA occurs when the airway partially or fully collapses during sleep, interrupting breathing multiple times per hour. CPAP machines deliver a steady stream of air pressure to help keep the airway open.
Because CPAP therapy is often used every night, many users rely on a heated humidifier to help prevent:
- Dry mouth
- Nasal irritation
- Throat discomfort
And this is where water purity matters.
Central and Complex Sleep Apnoea
While less common, CPAP machines may also be used for:
- Central Sleep Apnoea (CSA) – when the brain does not consistently signal breathing muscles
- Complex (Mixed) Sleep Apnoea – a combination of obstructive and central types
Regardless of the diagnosis, if your CPAP machine includes a humidifier chamber, manufacturers typically recommend distilled water to prevent mineral build-up.
Other Conditions Where CPAP May Be Prescribed
In some cases, CPAP therapy may also be used for:
- Obesity Hypoventilation Syndrome
- Certain COPD-related breathing difficulties (when prescribed)
- Post-operative respiratory support
- Severe chronic snoring (in privately purchased units)
In all cases where humidification is used nightly, water quality affects maintenance, cleaning frequency and equipment lifespan.
Why Water Purity Matters for CPAP Machines
Tap water in the UK contains dissolved minerals — particularly in hard water areas.
Over time, these minerals can:
- Leave white residue in the humidifier chamber
- Increase cleaning frequency
- Contribute to limescale build-up
- Shorten the lifespan of internal components
Distilled water, by contrast, contains virtually no dissolved minerals.
This means:
- No limescale
- Less residue
- Easier cleaning
- Reduced long-term maintenance
👉 Shop high-purity UK-manufactured distilled water
Comparison Table: What Water Should You Use in a CPAP Humidifier?
Not all “clean” water is mineral-free. Here’s a quick comparison to help you choose the safest option for long-term CPAP humidifier use:
| Water type | Contains minerals? | Risk of limescale/residue | Recommended for CPAP humidifier? | Notes |
|---|---|---|---|---|
| Distilled water | No (virtually mineral-free) | Very low | Yes (best option) | Helps protect humidifier chamber and reduces cleaning |
| Tap water | Yes | High (especially in hard water areas) | Not ideal long-term | Often causes white residue and limescale build-up |
| Filtered water | Usually yes | Medium | Sometimes (short-term) | Filtration may reduce taste/impurities but often leaves minerals behind |
| Bottled spring/mineral water | Yes (often more minerals) | High | Not recommended | Can accelerate residue build-up |
| Boiled water | Yes | High | Not recommended | Boiling kills some bacteria but does not remove minerals |
👉 For daily CPAP use, distilled water is the safest and simplest choice:
How Much Distilled Water Does a CPAP User Need?
Most CPAP humidifiers use approximately 200–400ml per night, depending on humidity settings.
- A 5L container lasts roughly 12–25 days
- A 25L container can last 2–4 months
- Buying larger sizes reduces the need for frequent reordering
With free next working day delivery available, you can maintain consistent supply without interruption.
Can You Use Tap, Filtered or Bottled Water Instead?
Boiled water is not the same as distilled water.
Boiling may kill bacteria but it does not remove dissolved minerals, which can still leave residue in your humidifier chamber.
Filtered or bottled water may still contain:
- Calcium
- Magnesium
- Trace salts
If you're unsure how distilled water compares to other purified types, you may find this guide helpful:
👉 Distilled vs Deionised Water
Why Choose UK-Manufactured Distilled Water?
Not all distilled water is the same.
When choosing water for CPAP use, look for:
- Genuine distillation process
- Batch consistency
- UK production
- Technical documentation available
At The Somerset Clear Water Company, we manufacture our distilled water in-house at our Somerset facility, supplying both home users and commercial clients.
👉 View our technical documentation:
Final Thoughts
CPAP therapy is often a long-term commitment. Using the correct water is a small step that can significantly reduce maintenance, protect your equipment, and improve comfort over time.
