Why Everyone Keeps Nagging You About Using Distilled Water in Your CPAP Humidifier

Let’s be honest…

If you’re a CPAP user, you’ve probably rolled your eyes at least once at the “only use distilled water” instruction. It’s right there on the label, in your user manual, and maybe your sleep technician even reminded you (again).

You might be thinking, “Really? How bad can tap water be?”Well, here’s why the nagging actually makes sense — and how ignoring it could quietly cost you more than you think.

💧 What’s the big deal about distilled water?

Distilled water is water that’s been boiled into steam and then condensed back into a liquid, leaving behind minerals, salts, and impurities.That means it’s pure H₂O — and nothing else.

Your CPAP humidifier uses warm water to add moisture to the air you breathe at night. When you use anything other than distilled water, the minerals and contaminants in regular tap or bottled water can:

• Build up white, chalky residue inside your humidifier chamber

• Clog your tubing and mask vents over time

• Shorten your machine’s lifespan by corroding delicate parts

• Provide a breeding ground for bacteria and mold if residue remains in the chamber

  
  

💧 Distilled vs. Reverse Osmosis Water — What’s the Difference?

Many people assume that the small filtered water tap in their kitchen — usually connected to a reverse osmosis (RO) system — produces water just as good as distilled.It’s close, but not quite the same thing.

Type of Water	How It’s Made	Purity Level	Contains Minerals?	Safe for CPAP?
Distilled Water	Boiled and condensed steam	99.9% pure	❌ No	✅ Best option
Reverse Osmosis (RO) Water	Forced through semi-permeable membrane	~95–98% pure	⚠️ Small traces may remain	⚠️ Acceptable short-term, not ideal long-term
Tap Water	Straight from municipal supply	Varies widely	✅ Yes	❌ Avoid

RO systems remove a lot of impurities and minerals, but not everything.Some microscopic minerals, chlorine byproducts, and even bacteria can pass through or re-enter the water from the storage tank and plumbing.

In contrast, distillation eliminates everything — minerals, metals, and microorganisms. That’s why CPAP manufacturers like ResMed and Fisher & Paykel specifically recommend distilled water only.

If you’re stuck without distilled water for a night or two, RO water is better than tap, but still not perfect for long-term use.

🦠 Tap water looks clean… but it’s not CPAP-clean

Even crystal-clear tap water contains trace minerals like calcium, magnesium, and iron.When heated nightly in your CPAP’s humidifier, these minerals don’t just evaporate — they stick, harden, and slowly create a crusty mineral film that’s impossible to fully remove.

Once that happens, your water chamber may start looking cloudy or stained. That’s not just cosmetic. Those spots can trap moisture and bacteria — not exactly what you want in the air you’re breathing 8 hours a night.

⚙️ The long-term damage nobody talks about

Replacing a CPAP humidifier chamber costs far more than a few litres of distilled water.Over time, mineral deposits can affect the sensor that regulates temperature and humidity levels, causing inaccurate readings and inconsistent therapy comfort.

In short:Skip distilled water → build-up → bacteria → bad smells → machine damage → expensive replacement.

💸 The small cost that saves a lot

Let’s do some quick math:

• Average distilled water: ±R100 for 5L (often lasts weeks)

• CPAP humidifier chamber replacement: R1 000 – R1 800

• New CPAP machine: from R14 000 upward

Using distilled water isn’t nagging — it’s smart economics.

🌙 What if you forget once or twice?

Relax — using tap or RO water once in an emergency won’t destroy your CPAP.But make sure you empty the chamber in the morning, wipe it clean, and refill with distilled water the next night.The key is consistency, not panic.

🧼 Bonus tip: Keep your humidifier chamber fresh

• Empty and dry it every morning

• Wash it with mild soap weekly

• Replace it every 6–12 months (or sooner if it turns cloudy or pitted)

• 
  

🌿 Final thoughts

Using distilled water may feel like a small hassle, but it’s one of the simplest ways to keep your therapy clean, safe, and effective.Think of it this way: your CPAP delivers pure air — so it deserves pure water.