You can use tap water in your CPAP humidifier for one emergency night—but you absolutely should clean the chamber thoroughly the next morning. All major manufacturers (ResMed, Philips Respironics, Fisher & Paykel) explicitly recommend distilled water only, and documented medical cases show why: a 67-year-old woman developed life-threatening Legionella pneumonia requiring ICU admission directly from tap water in her CPAP equipment, according to a 2017 case report in the Journal of Clinical Sleep Medicine.
About 24% of Americans use tap water in CPAP machines, according to a 2021 CDC survey, and 33% incorrectly believe tap water contains no bacteria. Meanwhile, waterborne pathogens from home medical devices cause an estimated 120,000 hospitalizations and 7,000 deaths annually in the US. Your stomach acid kills bacteria in drinking water, but aerosolized water vapor from a CPAP carries those same bacteria directly into your lungs.
⚠️ Why Manufacturers Demand Distilled Water
Mineral buildup happens fast—within 2-3 days of regular tap water use in hard water areas. Those minerals—primarily calcium and magnesium—form scale on the heating plate, reducing efficiency and forcing earlier equipment replacement. But equipment damage is the lesser concern.
🚨 The Real Risk Is Bacterial Infection: Tap water contains Legionella, Pseudomonas aeruginosa, and nontuberculous mycobacteria. Your CPAP humidifier provides exactly what they need: warmth, moisture, and 6-8 hours nightly to colonize plastic surfaces. Then you inhale the aerosolized bacteria directly into your airways. :::
Documented medical cases:
- 2017 Legionella case: 67-year-old woman with life-threatening pneumonia requiring ICU. Investigators found the same bacterial strain in both her sputum and CPAP equipment.
- 2025 Pseudomonas case: 57-year-old man with COPD developed pneumonia after "poor CPAP maintenance" with "green-colored growth on his mask."
These aren't theoretical risks—they're published medical case reports with real patients.
🆘 What to Do If You Use Tap Water for One Night
If you're in a bind without distilled water, tap water is manageable—but follow this protocol:
Immediate next steps:
- Empty the humidifier chamber first thing in the morning
- Wash thoroughly with mild soap and warm water
- If visible mineral deposits appear, soak in 1 part white vinegar to 3 parts water for 20 minutes
- Rinse thoroughly and air dry completely
- Resume distilled water immediately
💡 One Night = Acceptable Risk: One night with tap water followed by thorough cleaning won't cause catastrophic harm. Regular tap water use for weeks or months? That's when biofilm establishes and documented pneumonia cases occur. :::
🔄 Your Best Alternatives When Distilled Water Isn't Available
Option 1: Skip the humidifier for a night (Best choice)
Your CPAP machine still delivers therapy without the humidifier function. You'll experience dry mouth, but that's uncomfortable, not dangerous. Many CPAP users travel this way routinely.
Option 2: Boiled tap water (cooled completely) (Second best)
Boiling tap water for 1 minute (3 minutes above 6,500 feet elevation) kills bacteria per CDC guidelines. The limitation: Boiling removes bacteria but NOT minerals. You'll still need thorough cleaning the next day.
Option 3: Purified bottled water (Third choice)
Check the label for "purified water" with "no minerals added." Avoid spring water (high in minerals) and mineral water. Learn the difference between tap water and distilled water.
⚠️ Never Use: Spring water, well water (unless emergency and boiled), or softened water (high sodium). :::
🧼 The Cleaning Routine That Prevents Infection
Every morning:
- Empty remaining water (never reuse)
- Wipe chamber with clean cloth
- Air dry completely
Every week:
- Hand wash chamber with mild dish soap and warm water
- OR top-rack dishwasher (not above 131°F)
- Wash mask and headgear, rinse thoroughly
Every 2 weeks:
- Soak chamber in 1 part white vinegar to 3-5 parts water for 10-30 minutes
- Rinse thoroughly and air dry
Never use: Bleach or ozone-based cleaners. The FDA specifically warns against ozone CPAP cleaners.
💰 The Math on Distilled Water vs Equipment Damage
You save $39 per year using tap water. You risk $500-25,000 in costs.
⚖️ What Using Tap Water Does to Your Warranty
ResMed's warranty excludes "water ingress." While not explicitly mentioning tap water, mineral-caused equipment failure could void warranty claims. Your CPAP machine costs $500-1,000 out-of-pocket. A 5-year supply of distilled water costs less than one warranty-voiding repair.
🏥 The Medical and Manufacturer Consensus
The evidence is unambiguous: distilled water is the only water recommended by all manufacturers, medical authorities, and the CDC. For healthy adults, one emergency night with boiled tap water won't cause catastrophic harm—but it requires thorough cleaning and immediate return to distilled water.
ℹ️ Why Distilled Water? Distilled water has been heated to steam and condensed, removing minerals, bacteria, and impurities. It's not the same as filtered or purified water. Learn how to make distilled water at home. :::
Where to buy distilled water:
- Grocery stores: $0.99-1.99 per gallon
- Pharmacies: Available in medical supply section
- Online bulk: 6-12 gallons delivered monthly
- Annual cost: ~$39 for nightly CPAP use
Distilled water costs $39 per year. Don't compromise life-saving sleep apnea treatment by introducing bacterial pneumonia risks through contaminated water.
🔍 How Water Quality Varies by Location
Water hardness and contamination levels vary dramatically by region. Hard water areas (above 180 mg/L calcium carbonate) will cause mineral buildup faster. Cities with older infrastructure may have higher bacteria counts.
Check your city's water quality data to understand your local tap water composition. Even if your city has excellent water quality for drinking, the same water can harbor bacteria that become dangerous when aerosolized directly into your lungs through CPAP equipment.
📋 Quick Reference Guide
| Scenario | Use Distilled? | Alternative | Required Action |
|---|---|---|---|
| Normal use | ✅ Yes | None | Regular cleaning schedule |
| Emergency (1 night) | ⚠️ Boiled tap OK | Skip humidifier better | Deep clean next morning |
| Traveling | ✅ Yes | Purified bottled water | Check label carefully |
| No water available | Skip humidifier | Use CPAP without humidity | Dry mouth is safe |
| Regular tap water use | ❌ Never | Stop immediately | Replace chamber if buildup |
The bottom line: For one emergency night, carefully boiled and cooled tap water followed by thorough cleaning is acceptable. For regular use, only distilled water protects your health and equipment investment.