Only Use This Type Of Water In Your Humidifier (Explained)

Ile Kauppila

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Ile Kauppila

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Josh Mitchell

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When I got my first humidifier, I made a huge mistake. I used tap water in it. Soon, my room had mold on the windowsills and I got serious breathing problems.

So why did that happen?

It’s all because I used the wrong type of water. Tap water is simply poison for humidifiers.

I wrote this guide to help you avoid my mistake. Read on and I’ll tell you what kind of water is best for humidifiers — and why it’s not tap water.

Key Takeaways

  • Never use tap water in your humidifier. They have the highest chance of bacterial contamination and have a high mineral concentration.
  • Distilled water is the best choice for humidifiers followed by purified water (reverse osmosis).
  • Boiled water may seem like a good idea, but it has the highest mineral concentration.

Types Of Water Used In Humidifiers (Ranked For Safety)

You can, strictly speaking, use various types of water in your humidifier, but some of them can harm you and the machine. So, what type of water should you use?

One type is clearly superior to others.

Here’s my breakdown of the different types of water, conveniently ranked by safety.

1. Distilled Water – The Purest Form Of Water

Distilled water has been treated to remove all bacteria, minerals, and other contaminants. It’s the purest water available and the best choice for a humidifier.
Distilled water for humidifiers

During distillation, water is boiled so it turns into steam.

The gasification detaches all minerals, sediments, and impurities from the water, while the boiling process kills all microorganisms.

The steam vapor comes into contact with a cold, sterilized surface where it condenses.

The condensed, distilled water drips into a clean collection dish, which is bottled and sold.

The purity of distilled water reduces the chance of bacteria and mold growth and prevents any damage to the humidifier.

The unit can operate more smoothly and add only pure water to indoor air. I recommend using only distilled water in your humidifier.

TL;DR: Distilled water is the most ideal choice. It is sterilized and contains no contaminants / pollutants.

2. Purified Water – Almost Pure Water

Purified water is my #2 choice for a humidifier.

It’s filtered to remove minerals, bacteria, and other impurities, making the water almost perfectly pure.

The most common water purification method is reverse osmosis.

Water is forced through a semi-permeable membrane, which traps most impurities and contaminants. (1)

Not all purified water undergoes reverse osmosis.

Other purification methods include carbon, ultra-, and microfiltration, in addition to UV treatment. All the processes have the same end result — 99% pure water.

Important Note:

Purified water may have tiny amounts of minerals left.

I’ve never heard of them harming a humidifier.

In fact, this water type prevents mineral build-up, improving the longevity of your humidifier.

TL;DR: A great choice, but may have small traces of mineral deposit.

3. Demineralized Water – Workable Option But Not The Most Ideal

Demineralized water can be another good choice for humidifiers. It’s made by filtering water through a mesh membrane, which removes almost all of the minerals from it.

If you can’t find purified or distilled water, I can recommend demineralized stuff.

Some bacteria may remain in demineralized water, depending on the filtering process.

However, their amounts are generally small enough not to cause any harm in a humidifier.

TL;DR: While demineralized water does not have mineral content, it may contain micro organisms such as bacteria.

4. Bottled Water – Can Damage Your Humidifier

Bottled water is filtered and treated to make it safe to drink, but it still contains dissolved minerals.

They make the water taste great but can damage your humidifier.

During treatment, bottled water is exposed to UV light to kill bacteria. It’s also filtered to remove impurities, but the filters aren’t as fine as with more thorough processes.

This is so the flavorful dissolved minerals remain in the bottled water.

If you put bottled water in a humidifier’s tank, you may see mineral build-up on the unit’s inner parts and water filters.

This can make the humidifier less effective and even break it. I would avoid using bottled water in a humidifier.

TL;DR: Bottled or drinking water does not have micro organisms or bacteria, but it does have mineral concentration.

5. Boiled Water – High Mineral Concentration Can Cause Damage

Putting boiled water in a humidifier is not smart. You may think it’s safe, but boiled water can be very bad for your humidifier.

I know boiling water kills bacteria, but it also causes some water to evaporate.

Important Note:

As steam evaporates, the amount of water in your pot reduces, increasing the mineral concentration.

The high mineral content can easily cause deposits and limescale build-up in your machine, which is why you shouldn’t use boiled water in your humidifier.

You also definitely shouldn’t try putting boiling water in a humidifier!

That is dangerous both for you and the machine.

Read more in my article on whether to put hot or cold water in a humidifier.

TL;DR: Boiled water has a very high mineral concentration. It can damage the humidifier and spew white dust.

6. Tap Water – Not Recommended At All

Do not use tap water in humidifiers! I found this out the hardest possible way.

Tap water contains sediments, minerals, and bacteria that can damage your humidifier and impact your health.

Tap water is not ideal for humidifiers

The sediments and minerals in tap water will build up in your humidifier over time.

They will eventually prevent it from functioning correctly and the bacteria will spread through your home.

I strongly recommend not putting tap water into a humidifier. If you want to use tap water, distill it before pouring it into your humidifier.

I’ll tell you how to distill tap water later, so keep reading!

TL;DR: Stay way from tap water!

Summary Of Types Of Water For Humidifiers

Type of Water



– No Bacteria
– No Minerals
– #1 Choice of water for humidifiers


– No Bacteria
– Low Mineral Concentration
– #2 Choice for Humidifiers


– Some Bacteria
– No Minerals
– Not Ideal for humidifiers

Bottled Water

– No Bacteria
– Moderate Mineral Concentration
– Can cause mineral build-up

Boiled Water

– No Bacteria
– High Mineral Concentration
– Several mineral build-up

Tap Water

– Low-High Bacteria
– High Mineral
– Stay Away!

Distilled Water: Why Is It The Best Choice For Humidifiers?

Distilled water is the best water choice for any humidifier including the popular ultrasonic or evaporative humidifiers.

It has no minerals or bacteria, which benefits both your humidifier and your health.

Let’s look deeper, though. Here’s my breakdown of why distilled water is the best water for both a cool mist and a warm mist humidifier.

Prevents Mineral Deposits

Distilled water prevents mineral build-up inside your humidifier.

Non-distilled or hard water can contain minerals, like calcium, sodium, and magnesium. They will build up in the internal parts over time.

The mineral deposits force the unit to work harder and shorten its lifespan.

They could also clog important tubes or nozzles, preventing the humidifier from working altogether.

My first humidifier started losing effectiveness within a couple of months.

With distilled water, it’s far less likely minerals will build up inside your humidifier.

Your machine will work longer and you’ll save money when you won’t have to replace the unit as soon.

TL;DR: Distilled water has no minerals which increases the lifespan of the humidifier, prevents clogging of different components, and reduces chances of white dust build up.

Prevents Mold And Bacterial Growth

Distilled water is sterilized and has no unwelcome contaminants lurking in it.

Tap water and other less clean water types could carry mold spores or bacteria.

As the water sits in the humidifier, these contaminants can start breeding and grow inside the device.

Your humidifier can then spread them all over your home, which can produce negative health effects and mold build-up on walls and furniture — just like what happened to me.

Distilled water has no bacteria in it, so you won’t have to worry about your humidifiers turning into bacterial breeding grounds.

However, you still must remember to keep your humidifier clean.

TL;DR: Distilled water is sterilized and thus carries no risk of spreading diseases and micro organisms such as mold or bacteria.

Improves Air Quality

Naturally, any pathogens in a humidifier’s water will make your indoor air less healthy.

Additionally, the minerals present in the water could turn into fine white dust as the water vapor evaporates in the air.

This dust can cover your furniture and cause respiratory problems. I got serious breathing issues from the dust.

Distilled water has no minerals or bacteria, which helps prevent problems like asthma, sinus issues, and coughing. You can breathe easier and enjoy higher air quality.

TL;DR: Distilled water keeps the air not only moisturized but also provides the best possible health benefits you can get from a humidifier.

How Can You Make Distilled Water At Home?

I recommend buying bottled distilled water for your humidifier — it’s just so much easier.

You can distill water yourself, though, with some effort.

Here are three methods I’ve used to distill water at home.

Rainwater Method – Best If You Receive Plenty Of Rainfall

The rainwater method isn’t a true distillation method. It’s also slow and less reliable, but it takes less effort than the others.

  1. Gather rainwater in a large container over a few days, weeks, or months (depending on your climate).
  2. Move the filled rainwater container to a covered, clean location.
  3. Let the container sit for 48-72 hours to allow sediment to fall to the bottom.
  4. Siphon the surface water out carefully, avoiding the sediment.

TL;DR: Rainwater method is cheap and effortless, but there are chances of contamination.

Glass Bowl Method – The Easiest In-Home Method

The glass bowl method is the easiest way to distill water at home.

You need a large pot with a glass lid, a glass bowl that fits inside the pot, and some ice.

  1. Fill the bowl halfway and place it on a stove.
  2. Set the glass bowl to float inside the pot.
  3. Place the lid upside down above the bowl.
  4. Pour ice onto the inverted lid.
  5. Turn the hob on and bring the water to a boil.
  6. Water evaporates and condensates on the lid, dripping into the bowl.
  7. Refill the lid with ice as needed until all the water is distilled.

TL;DR: This is an easy and recommended method for most users.

Glass Bottle Method – Challenging But Offers Best Results

The glass bottle method is challenging, but it can produce the purest water.

You need a pot, ice, and two heat-proof bottles — one with a straight and one with a curved neck.

  1. Fill the straight-necked bottle halfway with water.
  2. Attach the bottles to each other mouth-to-mouth with heat-proof duct or masking tape.
  3. Place the straight-necked bottle in the pot at a 30-degree angle.
  4. Surround the curved-neck bottle with ice to chill it.
  5. Heat the pot and straight-necked bottle on a stove until the water boils.
  6. Carefully detach the bottles once all the hot water has condensed into the curved-neck bottle.

TL;DR: Glass bottle method requires some effort but it is the most effective way of extracting of distilled water.

What Kind Of Water Is Best For A CPAP Humidifier?

I, and manufacturers of CPAP humidifiers, recommend using only distilled water to help protect your health.

A Continuous Positive Airway Pressure (CPAP) humidifier is a specific type of humidifier designed for sleep apnea patients.

It delivers a continuous flow of pressurized air directly to your nose and mouth to help you breathe overnight. (2)

A humidifier works alongside the CPAP unit to keep the air from drying and impacting your breathing. It also helps prevent condensation within the tubes.

Important Note:

A CPAP humidifier can have a huge positive health impact and may prevent infections, nasal congestion, inflammation, and even nosebleeds.

Using tap water in the machine could pump microbes, bacteria, and minerals directly into your nasal passages.

This could seriously endanger your health by causing breathing problems and infections.

Unlike tap water, distilled water is free from any contaminants that can impact your health.

Change the water daily when using a CPAP device, and it can tremendously improve your health and sleep quality.

TL;DR: Just as with any humidifier, it is ideal to use distilled water with CPAP humidifiers. 


How Long Do You Have To Boil Water For It To Be Distilled?

You have to boil tap water for about 45 minutes to get a sufficient amount of distilled water.

However, tap water becomes distilled immediately as soon as it turns into steam and re-condenses.

How Long Do You Have To Boil Water To Kill Bacteria?

You must boil tap water for 1-3 minutes to kill bacteria. The length of time depends on the altitude you live in. (3)

Can I Use Rainwater Instead Of Distilled Water?

You can use rainwater instead of distilled water in a humidifier. However, rainwater may still contain impurities, so distilled water is the best choice.

What Is The Difference Between Purified, Distilled, And Spring Water?

The difference between purified, distilled, and spring water is their level of dissolved minerals.

Distilled water has no contaminants or minerals and is best for humidifiers. Purified and spring water are filtered but may still contain minerals.

How Often Should You Change The Water In A Humidifier?

You should change the water in a humidifier every day to prevent mold and bacteria growth.

You should also change your humidifier’s filter regularly and clean it weekly.

So, Which Water To Use?

To be blunt, you shouldn’t use anything but distilled water in your humidifier — especially not tap water.

I know from bitter experience that tap water is your ticket to mold growth, health issues, and a broken humidifier.

A humidifier is only as good as the water you use. With pure, contaminant-free water in a humidifier, you can safely and effectively add humidity to your home.


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Ile Kauppila

MA Multimedia Journalism / BA English Philology

Ile Kauppila
Ile Kauppila is a globetrotting writer and editor living in Virginia. Ile holds an MA degree in Multimedia Journalism and a BA in English Philology. Ile has written for a variety of home, HVAC, and energy-related websites and publications. He has covered HVAC solutions, insulation, and energy-efficient construction, automotive AC systems for multiple auto dealerships and garages.

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