You can make distilled water for your CPAP machine at home using nothing more than a large pot, a smaller collection bowl, an inverted lid, and a stovetop burner. The process works by boiling water into steam and then condensing that steam back into liquid, leaving behind minerals, chemicals, and other dissolved solids. A countertop electric distiller does the same thing with less babysitting. Either approach produces water clean enough for a CPAP humidifier, though how you store and handle that water matters just as much as how you make it.
Why Your CPAP Needs Distilled Water
Most CPAP machines with built-in humidifiers heat a small reservoir of water to add moisture to the air you breathe overnight. When that water contains dissolved minerals, as virtually all tap water does, those minerals get left behind as the water evaporates. Over time you see a white or yellowish crust coating the inside of the chamber. That mineral buildup is more than cosmetic. It can reduce the efficiency of the humidifier, make the chamber harder to clean, and shorten the life of the equipment.
The bigger concern is what you’re inhaling. Research on ultrasonic humidifiers, which aerosolize water in a broadly similar way, has shown that dissolved minerals and metals in fill water end up as fine airborne particles. Those particles can be small enough to reach the deep lung, where they may trigger inflammatory responses.
CPAP heated humidifiers work differently from ultrasonic units (they evaporate rather than mechanically nebulize), so they produce far fewer mineral-laden aerosol particles. Still, the general principle holds: the cleaner the water going in, the cleaner the air coming out. Distilled water has virtually zero dissolved solids, which is why every major CPAP manufacturer recommends it.
The Stovetop Distillation Method
Home distillation sounds like chemistry-lab stuff, but the setup is remarkably low-tech. You need a large stainless-steel pot with a domed or concave lid, a heat-safe glass or stainless-steel bowl that fits inside the pot without touching the bottom, and a bag of ice. That’s the whole rig.
Here’s how it works:
- Fill the pot: Add tap water until it’s roughly half full. Place the collection bowl inside so it floats or rests on a small rack above the water line. The bowl should not be submerged.
- Invert the lid: Place the pot lid upside down on top of the pot so the handle points downward into the interior. This creates a concave surface on top where steam will condense and drip into your collection bowl.
- Heat to a gentle boil: Bring the water to a simmer or low boil. You don’t need a rolling boil; a steady simmer produces steam without splashing tap water into your collection bowl.
- Add ice on top: Pile ice on the inverted lid. The cold surface speeds condensation dramatically. As steam rises, it hits the cold lid, turns back into liquid water, runs down the dome, and drips off the handle into the bowl below.
- Collect and cool: After 30 to 45 minutes you’ll have a meaningful amount of distilled water in the bowl. Carefully remove the bowl (it will be hot), let it cool, and transfer the water to a clean container.
This method works, but it’s slow. You’ll typically collect enough water for one or two nights of CPAP use per session. You’ll also need to replenish the ice periodically and keep an eye on the stove. It’s a good option when you’re in a pinch or want to avoid buying a machine, but it’s not practical as a daily routine for most people.
Countertop Electric Distillers
If you use a CPAP every night, a countertop distiller pays for itself within a few months compared to buying jugs of distilled water. These appliances typically cost between $80 and $200 and work on the same principle as the stovetop method: a heating element boils water in a chamber, steam travels through a vent or coil, condenses, and drips into a collection carafe. Most models produce about a gallon in four to six hours and shut off automatically when the boiling chamber runs dry.
A few things to know before buying one. Countertop distillers use a fair amount of electricity, roughly comparable to running a coffee maker for several hours. They also generate heat, which matters if you’re running one in a small kitchen during summer. Many models include an activated-carbon filter at the outlet to catch volatile organic compounds that evaporate and condense along with the water. Those filters need periodic replacement, usually every one to three months depending on usage. Check whether replacement filters are readily available for the model you’re considering before you buy.
The water that comes out of a well-functioning countertop distiller is essentially the same product as what you’d buy in a store-brand jug. For CPAP purposes, it’s more than adequate.
How to Tell If Your Homemade Water Is Clean Enough
Distilled water should have close to zero dissolved solids. The easiest way to verify this is with an inexpensive TDS (total dissolved solids) meter, a pen-sized device you dip into a water sample. These meters measure electrical conductivity and convert it to a parts-per-million reading. Store-bought distilled water typically reads between 0 and 5 ppm. Your homemade distilled water should land in a similar range. Tap water, for comparison, usually falls somewhere between 50 and 500 ppm depending on your municipal supply.
Inexpensive TDS meters have been shown to be reasonably accurate for this purpose. A study evaluating a low-cost TDS sensor found calibration errors of less than 1% at the 500–1000 ppm range, which means at the very low readings you’re checking for, the meter will reliably tell you whether your water is clean or not.1International Journal of Sustainable Development Goals. A Cost-Effective Instrument for Measuring Total Dissolved Solids, Electrical Conductivity and Turbidity – A Step towards Sustainable Development You can pick one up for under $15 at most hardware or aquarium stores. If your reading creeps above 10 ppm, something went wrong: tap water may have splashed into your collection bowl, or your distiller’s boiling chamber needs descaling.
A TDS meter won’t detect bacteria or volatile chemicals, though. It’s a mineral purity check, not a sterility test. For CPAP purposes, mineral purity is the main concern, but proper storage and handling matter for the biological side.
Storing Your Distilled Water Without Ruining It
Making the water is only half the job. Contamination during storage can undo your effort. Distilled water is actually more vulnerable to bacterial growth than you might expect, because it lacks the residual chlorine that keeps tap water relatively stable in the short term.
Research on stored water in different container types has found that bacterial colony counts climb rapidly, especially in plastic bottles. One study found that water stored in plastic bottles at refrigerator temperature reached colony counts above 100,000 per milliliter within a week, while glass bottles held bacteria to roughly a tenth of that level.2Elsevier / International Journal of Food Microbiology. The bacterial flora of non-carbonated, natural mineral water from the springs to reservoir and glass and plastic bottles That study looked at mineral water rather than distilled water, and distilled water has fewer nutrients for bacteria to feed on. Even so, the takeaway is practical: use clean glass containers with tight-fitting lids when possible, refrigerate what you won’t use within a day or two, and don’t store homemade distilled water for weeks on end.
Before filling your storage container, wash it thoroughly with hot soapy water and rinse with some of the distilled water itself, not tap water. If you’re using a countertop distiller that drips into its own glass carafe, transfer the water to a sealed container promptly rather than leaving it sitting open on the counter where dust and airborne bacteria can settle in.
What Actually Happens If You Use Tap Water
On a single night, nothing dramatic. Your CPAP will work fine. You’ll breathe humidified air. The sky won’t fall. The problems with tap water are cumulative: mineral scaling that builds over weeks, a reservoir that becomes harder to clean, and the slow introduction of aerosolized mineral particles into your airway.
Systematic reviews of ultrasonic humidifier use have found clear proportional relationships between dissolved mineral and microbial concentrations in fill water and the levels of those same contaminants in the air the device emits.3PubMed Central. Exposure at the indoor water-air interface: Fill water constituents and the consequent air emissions from ultrasonic humidifiers: A systematic review Again, CPAP heated humidifiers don’t aerosolize water the way ultrasonic humidifiers do, so the risk is lower. But the direction of effect is the same: dirtier water in, more stuff in the air you breathe.
Fine aerosolized particles from mineral-laden water can penetrate into the lower lung and even cross into the bloodstream.4PubMed Central. An overlooked route of inhalation exposure to tap water constituents for children and adults: Aerosolized aqueous minerals from ultrasonic humidifiers Case reports linked to humidifier-type devices have included hypersensitivity pneumonitis in adults and children.3PubMed Central. Exposure at the indoor water-air interface: Fill water constituents and the consequent air emissions from ultrasonic humidifiers: A systematic review Those cases involved ultrasonic humidifiers, not CPAP machines specifically, and the exposure patterns are different. But for someone breathing through a humidified airway device for seven or eight hours every night, the accumulated exposure over months and years adds up in ways that occasional humidifier use does not.
The Infection Risk Is Real but Specific
Beyond minerals, there’s the bacterial angle. The warm, moist environment inside a CPAP humidifier chamber and tubing is a hospitable place for microorganisms if the equipment isn’t maintained. At least one documented case involved a patient who developed severe Legionella pneumonia traced to her CPAP equipment. She tested positive for Legionella antigen and was admitted to intensive care. Investigators from the state health department concluded the infection likely came from the CPAP setup, which had not been cleaned appropriately.5PubMed Central. A case of legionella pneumonia caused by home use of continuous positive airway pressure
Before that scares you into throwing out your machine, some perspective. A survey of respiratory devices in long-term care facilities, including CPAP units, BiPAPs, oxygen humidifiers, and ventilators, tested 72 swabs across 24 devices and found no Legionella bacteria in any of them.6ScholarWorks. The Presence of Legionellae in Respiratory Devices: Convenience Sampling of Idaho Long Term Care Facilities The researchers concluded that Legionella is probably not lurking inside respiratory devices under normal circumstances, separate from an active outbreak in the water supply. The case reports that do exist tend to involve equipment that went a long time without cleaning, combined with a contaminated water source.
The practical lesson: using distilled water reduces but does not eliminate infection risk. You still need to clean the humidifier chamber, tubing, and mask regularly. Most manufacturers recommend daily rinsing of the chamber and weekly washing with mild soap and water. Distilled water keeps minerals and most waterborne pathogens out of the system, but biofilm from your own breath and skin oils will accumulate on contact surfaces regardless of water quality.
Filtered, Bottled, and Boiled Water Are Not the Same
A common misconception is that any “purified” or “filtered” water is interchangeable with distilled water for CPAP use. It isn’t, and the differences matter.
- Boiled water: Boiling kills bacteria and other living organisms, but it does nothing to remove dissolved minerals. In fact, boiling concentrates minerals because some of the water leaves as steam while the minerals stay behind. Boiled-and-cooled tap water is still mineral-laden tap water.
- Carbon-filtered water: Pitcher filters and fridge filters primarily remove chlorine, some organic compounds, and improve taste. They do not meaningfully reduce dissolved mineral content. Your Brita pitcher is not making distilled water.
- Bottled spring water: Spring water is marketed for its mineral content. It’s often worse for a CPAP humidifier than plain tap water, depending on the brand.
- Reverse-osmosis water: This is the closest substitute. A good RO system removes the vast majority of dissolved solids, typically bringing TDS down to 10–30 ppm. That’s not as pure as distilled (0–5 ppm), but it’s far better than tap water and generally acceptable for CPAP use if distilled water is unavailable.
- Bottled “distilled” water: This is actual distilled water and works perfectly. The downside is cost and the environmental drag of single-use plastic jugs if you’re going through several per week.
If you’re traveling and can’t distill or buy distilled water, reverse-osmosis filtered water is your best backup. In a true emergency where no purified water is available, you can run your CPAP humidifier with tap water for a night or two and then thoroughly clean the chamber afterward. Many people also choose to skip the humidifier entirely for short trips rather than deal with water quality issues.
Skipping the Humidifier Altogether
Your CPAP machine does not require water to function. The humidifier is an add-on for comfort. If you turn it off or leave the chamber empty, the machine still delivers pressurized air to keep your airway open. What you lose is moisture, which for many users means waking up with a dry mouth, sore throat, or stuffy nose. Some people tolerate dry air fine, especially in humid climates. Others find it miserable enough that they stop using the CPAP altogether, which defeats the purpose of treating sleep apnea.
If the hassle of obtaining or making distilled water is a barrier to using your CPAP consistently, running it without the humidifier is vastly better than not using it at all. Untreated obstructive sleep apnea carries cardiovascular, metabolic, and cognitive risks that far outweigh any irritation from dry air. If you go the no-humidifier route and find the dryness intolerable, a heated tube (available for most modern CPAP models) can help by reducing condensation and rainout without requiring the humidifier to be cranked up as high.
Getting the Most from a Home Distillation Routine
If you decide to distill your own water regularly, a few habits make the process smoother. Batch your production: a countertop distiller running once or twice a week produces enough water for nightly CPAP use with some left over for other household uses like steam irons or nasal rinse. Keep two or three clean glass containers in rotation so you always have distilled water ready while a fresh batch is being made.
Descale your distiller or stovetop pot periodically. The minerals you’re removing from the water don’t vanish; they concentrate in the boiling chamber as a hard white crust. A soak with white vinegar or citric acid solution every few batches keeps the heating element efficient and prevents flakes of scale from contaminating future runs. If you use the stovetop method, inspect your collection bowl and lid between sessions. Any residue suggests tap water splashed in during boiling, which means you need to reduce heat or reposition the bowl.
Check your TDS reading every few batches as a quick quality-control step. If the numbers start creeping upward, it usually means the distiller needs cleaning, the carbon filter needs replacing, or your collection and storage routine has a contamination point somewhere. A consistent reading under 5 ppm means everything is working as it should.