How long does distilled water last for CPAP?

CPAP, or continuous positive airway pressure, machines are commonly used to treat sleep apnea. CPAP machines work by delivering constant airflow through a mask to keep the airway open during sleep. Distilled water is recommended for use in CPAP machines to prevent mineral buildup and bacteria growth.

Quick answers

Here are some quick answers to common questions about how long distilled water lasts in a CPAP machine:

  • Unopened distilled water can last indefinitely.
  • Opened distilled water lasts about 7-10 days in a CPAP machine.
  • Properly stored distilled water can last up to 6 months after opening.
  • Factors like temperature, cleanliness, and humidity can affect how long distilled water lasts.
  • Cloudiness, smells, or tastes indicate expired distilled water.

How does distilled water expire?

Distilled water is purified water that has been boiled and condenses to remove minerals, salts, and other impurities. This leaves pure H20 without additives like fluoride typically found in tap water.

Unopened, commercially purchased distilled water can technically last forever because it is sterile and sealed from contaminants. However, opened distilled water has a shorter shelf life. When exposed to air, distilled water lacks the minerals and impurities that prevent microbial growth in tap water. Over time, bacteria, fungi, and other microorganisms can start multiplying in the distilled water.

Additionally, opened distilled water absorbs carbon dioxide from the air, causing the pH to drop and become acidic over time. Plastic from the container can also leach chemicals into the water, compromising purity.

How long does opened distilled water last in a CPAP machine?

For CPAP use, most experts recommend changing and refilling the distilled water tank every 7-10 days. Here are some guidelines on lifespan:

  • 7 days: Replace distilled water in CPAP humidifier tank every 7 days for best quality.
  • 10 days: Distilled water may last up to 10 days but quality starts declining after a week.
  • 2 weeks: Change distilled water after no more than 2 weeks maximum.
  • 30 days: After 30 days, bacteria and mineral buildup are likely.

CPAP tanks provide a warm, moist environment perfect for microbe growth. Properly cleaning and disinfecting your CPAP equipment regularly is recommended to further prevent bacteria colonization.

How to make distilled water last longer

You can extend the shelf life of distilled water and minimize waste by:

  • Storing in an airtight container in a cool, dry place.
  • Avoiding extreme temperatures.
  • Only opening when ready to use.
  • Using clean pouring techniques to prevent contamination.
  • Cleaning CPAP tank regularly.
  • Monitoring water for signs it has expired.

Proper storage

The ideal storage conditions for distilled water involve:

  • Airtight container: Use the original container or an airtight sealable jug.
  • Cool environment: Store around 60-70°F to minimize microbial growth.
  • Dark space: Light promotes algae and bacterial growth.
  • Dry area: Avoid humid environments that introduce moisture.
  • No metal contact: Stainless steel can leach nickel and cadmium.

Avoid temperature extremes

Hot and cold temperatures will shorten how long distilled water stays fresh. Avoid:

  • Freezing: Causes chemical separation and container cracking.
  • Heat: Speeds up microbial multiplication and plastic leaching.
  • Direct sunlight: Exposure to UV light damages purity.

Use clean pouring techniques

Carefully pour distilled water directly into the CPAP tank to prevent contamination and maximize lifespan. Steps include:

  1. Do not directly drink from the storage container.
  2. Avoid allowing nozzle to touch tank opening.
  3. Use a clean funnel if available.
  4. Wipe and dry spouts before sealing containers.

Regular tank cleaning

Even with distilled water, CPAP tanks can accumulate microbes and minerals over time. Follow your device guidelines to regularly wash and disinfect all CPAP parts that contact water to optimize distilled water life. This will minimize bacteria that can multiply and contaminate the water.

How to tell when distilled water has expired

Watch for these signs that indicate distilled water has expired and needs changing:

  • Appearance: Cloudiness, particles, sediment
  • Odor: Smells stale, musty, or unpleasant
  • Taste: Salty, metallic, bitter, or acidic
  • CPAP issues: Tank/tube buildup, odd tastes in airflow

Cloudiness indicates microbial growth, while smells and tastes signal chemical changes from absorbed gases and compounds. If you notice any expired water signs, empty system and refill with fresh distilled water.

Can you reuse distilled water?

It is not recommended to reuse distilled water that has been sitting in a CPAP machine. The warm, humid conditions allow contamination even if the water still appears clear. However, you can reuse freshly opened distilled water for the following purposes:

  • Watering plants: Distilled lacks minerals but provides hydration.
  • Ironing: Distilled water prevents mineral buildup on iron plates.
  • Auto batteries: Distilled water can top up battery fluid when low.
  • Cleaning: For washing delicate jewelry or electronics prone to water spots.

Use your judgment – if the water has any smells, tastes, or clouding, it is safest to discard.

Is it safe to drink expired distilled water?

It is generally not recommended to drink distilled water from a CPAP machine if it has been opened and stored for more than a week. While not necessarily unsafe in small amounts, expired distilled water may contain multiplied microbes that can cause illness if ingested in large volumes. Stale distilled water also absorbs substances that impact taste and quality over time.

However, drinking expired distilled water in a survival situation is unlikely to cause harm. The most concern is contamination from the storage container or environment rather than the water itself. Letting questionable water stand uncovered overnight can allow chlorine gas to dissipate.

Can expired distilled water hurt your CPAP machine?

Yes, using expired distilled water in your CPAP can potentially damage your machine over time due to:

  • Bacteria: Microbes coat tubes and can clog airflow pathways.
  • Scale buildup: Minerals in expired water leave alkaline residue.
  • Mold: Fungi flourish in warm, moist tanks and machines.

For optimal CPAP function, change distilled water every 7-10 days. Always follow your manufacturer’s recommendations for cleaning and maintenance.

How much distilled water does a CPAP machine need?

CPAP machine water chambers typically hold between 150-300 mL of distilled water. However, exact fill lines vary by device. Check your CPAP equipment manuals for:

  • Tank capacity
  • Fill line locations
  • Recommended distilled water amounts

Underfilling prevents adequate humidification while overfilling can cause sputtering and water accumulation in tubes. Follow guidelines to add the proper volume of fresh distilled water each time you refill your CPAP device.

Can you use tap water in a CPAP machine?

Tap water is not recommended for CPAP machines. The minerals, chemicals, and impurities found in tap water can harm your device over time. Distilled water prevents scale buildup and provides optimal humidification. However, in an emergency, tap water can be used for a single night if distilled water is unavailable.

The risks of occasional tap water use include:

  • Mineral residue on machine parts
  • Bacterial growth in stagnant warm water
  • Odd smells or tastes from additives

To mitigate damage, use cold tap water and clean/disinfect your CPAP system thoroughly the next morning. Long-term tap water use will require descaling maintenance.

Distilled vs purified vs spring water in CPAPs

Various types of water may be used in CPAP machines, but distilled water is generally preferred. Here’s how the different kinds compare:

Water Type Mineral Content CPAP Recommended?
Distilled Zero minerals Yes
Purified Low minerals Yes
Spring Moderate minerals No
Tap High minerals No

While purified water contains more minerals than distilled, it can work well in CPAP machines when distilled is unavailable. Spring and tap water have too many dissolved solids that can leave mineral residue during humidification.


Why does distilled water expire so quickly?

Distilled water lacks the minerals and disinfecting agents found in tap water that prevent microbial growth. Over time, exposure to light, air, and bacteria reduce purity. Storage conditions greatly impact shelf life after opening.

How long can you store distilled water?

Unopened distilled water lasts indefinitely. Opened distilled water lasts 7-10 days in a CPAP machine. Properly stored distilled water lasts 3-6 months after opening.

Can I mix fresh and old distilled water?

It is not recommended to mix new and old distilled water in your CPAP. Empty tank fully and refill with 100% fresh distilled water to limit bacteria.

Why does my CPAP manual say distilled water only?

CPAP device manufacturers recommend distilled water because it will not leave behind mineral residue from the humidification process. Tap and mineral water can scale up machine parts.

What temperature should distilled water be for CPAP?

Room temperature distilled water around 60-70°F is best for CPAP use. Avoid very cold or hot distilled water as temperature extremes breed bacteria and impact performance.

The bottom line

Distilled water can last indefinitely unopened but use opened distilled water within 7-10 days in CPAP machines for best results. Properly stored and freshly poured, distilled water lasts up to 6 months. Watch for signs of cloudiness, smells, or tastes that indicate time to discard. Change distilled water frequently and clean CPAP equipment regularly to maximize lifespan.

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