Is distilled water required for use in the humidifier chamber of Positive Airway Pressure (PAP) machines?

Water Requirements for PAP Machine Humidifiers

For home CPAP/PAP machines used to treat obstructive sleep apnea, distilled water is recommended but sterile water is not required, as these convection-type humidifiers produce water vapor without aerosolizing the water itself. 1, 2

Key Distinction: Hospital vs. Home PAP Devices

The water requirements differ significantly based on the clinical setting and device type:

Hospital/Medical-Grade Respiratory Equipment

• Sterile water (not distilled, nonsterile water) must be used to fill bubbling humidifiers in mechanical ventilators and medical-grade respiratory devices 3
• This strict requirement exists because hospital ventilator humidifiers can aerosolize water, potentially transmitting bacteria directly into the lower respiratory tract 3
• Large-volume nebulizers and bubbling humidifiers pose the greatest infection risk and require sterile water 3

Home CPAP/PAP Machines for Sleep Apnea

• Distilled water is the standard recommendation for home CPAP humidifiers 1
• Research demonstrates that convection-type humidifiers used in CPAP therapy produce water vapor but do not aerosolize water, meaning bacteria cannot be transported into the airways 2
• One study using radioactive tracer confirmed no aerosol production at both low-flow (2-6 L/min) and high-flow (31-46 L/min) rates typical for CPAP 2

Evidence-Based Rationale

Why Distilled Water is Preferred for Home PAP

• Prevents mineral buildup in the humidifier chamber that can reduce device effectiveness and require more frequent cleaning 1
• Reduces maintenance burden compared to tap water, especially in hard water areas 1
• Manufacturer recommendations typically specify distilled water 1

Why Sterile Water is Not Required for Home PAP

• The convection-type humidifiers in home CPAP devices do not create aerosols that could carry microorganisms into the lungs 2
• Research specifically testing CPAP humidifiers found tap water to be a "probably safe alternative" for these devices 2

Important Caveats and Infection Risk Considerations

Cleaning Practices Matter More Than Water Type

• Inadequate cleaning of CPAP equipment poses greater infection risk than water choice 4, 5
• Patients using heated humidifiers who cleaned devices inadequately had significantly more upper airway infections (57.1% vs. 20%, p<0.05) compared to those who cleaned regularly 4
• Most home users report only weekly cleaning when daily cleaning is recommended 5

Bacterial Contamination Can Still Occur

• Even with proper water, contaminated humidifier water can harbor bacteria 6
• One study recovered bacteria from CPAP breathing tubes in 9 of 11 tests when humidifier water was contaminated, with counts ranging from tens to thousands of colony-forming units 6
• Hydrophobic breathing-circuit filters can prevent bacterial transmission from contaminated humidifier water 6

Practical Recommendations

For Home CPAP/PAP Users:

• Use distilled water as the standard choice 1
• Purified water is acceptable but may contain more minerals than distilled water 1
• Clean the humidifier chamber daily with soap and water to prevent bacterial colonization 5
• Empty remaining water daily rather than topping off 5
• Consider using a hydrophobic filter if concerned about infection risk 6

For Hospital/Medical Settings:

• Use only sterile water for mechanical ventilator humidifiers and bubbling humidifiers 3
• Never substitute distilled or tap water in these devices 3
• Follow strict protocols for equipment disinfection between patients 3

Common Pitfalls to Avoid

• Do not confuse home CPAP humidifiers with hospital ventilator humidifiers - they have different infection risks and water requirements 3, 2
• Do not use tap water in hard water areas as rapid mineral buildup will damage the humidifier chamber 1
• Do not assume "purified water" meets consistent standards - purification methods vary significantly 1
• Do not neglect daily cleaning regardless of water type used - inadequate cleaning poses greater infection risk than water choice 4, 5
• Do not reuse water from previous nights - empty and refill daily 5