What Is The Best Water for a Humidifier?

Humidifiers are a great way to fight dry air and support respiratory health, especially during dry winter months. But if you’re using the wrong kind of water in your humidifier, you could actually be doing more harm than good.

So, what is the best water for humidifiers?

Distilled water is the only type of water you should be using in your humidifier. Keep reading to learn why distilled is best and why you should not use other types of water in your humidifier.

water flowing from the faucet

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Why Distilled Water Is Best For Your Humidifier

distillation apparatus

Distilled water is pure H2O produced by boiling water and then collecting and condensing the steam. Unlike tap water and other types of bottled water, it does not contain any minerals or impurities. This fact makes it better for your humidifier for many reasons.

Won’t Cause Scale Build-Up

Scale or limescale is the technical term for the white, chalky build-up of calcium and magnesium. These two minerals are common in various types of water and especially prevalent in tap water.

These heavy minerals are left behind as water evaporates, either during heating or mist production.

Scale can be problematic in humidifiers because it can collect on the heating elements or nebulizers, reducing their effectiveness or stopping them from working altogether. Areas of scale build-up also provide the perfect habitat for mold and bacteria to congregate and grow.

Since distilled water doesn’t contain minerals, you won’t have to worry about scale build-up. It will also keep your dehumidifier cleaner and functioning better over time. 

Prevents Scale Dust

limescale build-up on a humidifier’s water tank

Mineral deposits aren’t just a problem inside your humidifier. You can also deal with a white, dusty scale that can be released into the air.

Scale dust released into the air will settle onto surfaces around the appliance, causing discoloration and potentially damaging electronics. Like scale build-up, this dust can be difficult to remove, especially from water-sensitive surfaces.

But the real threat of scale dust is more serious. 

Before this white dust settles on your furniture and appliances, it is airborne, which means there is a probability that you can inhale it. In large enough quantities, limescale dust has the potential to irritate the throat and lungs. With repeated exposure, it can even cause respiratory disease.

Note: In addition to calcium and magnesium, tap water can contain lead, silica, and other harmful minerals. These minerals are also known to be aerosolized in ultrasonic humidifiers. Once these particles are in the air, they can easily be breathed in and introduced to your body.

Helps Reduce Mold Growth

While mold spores exist just about everywhere and can be introduced into your humidifier no matter what type of water you use, distilled water is least likely to contribute to mold growth.

Distilled water is purified of all contaminants, meaning you won’t be introducing any additional mold into your system. And, because this water is free of minerals, it won’t create any scale deposits that mold can cling to.

Note: By cleaning your humidifier thoroughly and using only distilled water, you can keep mold growth to a minimum and prevent mold spores from being released into the air.

Regardless of what kind of water you use, mold build-up in your home can be an issue if your home humidity levels are too high. If this is the case in your home, turn off the humidifier and consider investing in a dehumidifier instead.

Free of Organic Contaminants

woman sneezing

Mold isn’t the only contaminant that can be released into the air.

Viruses, bacteria, and other organic contaminants are also present in tap water and even spring water. Ultrasonic humidifiers are especially prone to aerosolizing these contaminants and spreading them through your home. Depending on the nature of these contaminants, you could get seriously ill from breathing them in.

Bacteria like Serratia marcescens, the microbe responsible for the pink mildew in your shower, is another microorganism that thrives in humidifiers. This common bacteria is known to cause different health issues, from urinary tract infections to pneumonia. These risks are increased in people who are exposed to aerosolized S. marcescens.

By keeping your humidifier clean and using only distilled water, you can significantly reduce the likelihood of bacterial growth inside the unit. It will also lower the overall number of organic contaminants released into the air. 

Can You Use Boiled Water In a Humidifier?

boiling water

By boiling water for at least one minute, you effectively kill all bacteria, viruses, and other pathogens. Unfortunately, boiling water does nothing to reduce the mineral content. In fact, because some of the water is evaporated during the boiling process, the mineral content ratio is actually increased.

Using boiling water in a humidifier is more likely to result in limescale build-up and scale dust release. While the water will be free of bacteria and mold, these contaminants can find their way into your unit through air or surface contact. Once inside, they can quickly multiply using the scale surface as their breeding grounds. 

So, no. You shouldn’t use boiled water in your humidifier.

Can You Use Filtered Water In a Humidifier?

a person getting filtered water

Water filters use different means to remove impurities from tap water. These filter systems typically target minerals, large bacteria, odors, and chemicals like chlorine.

While filtered water will have a lower mineral content than tap water, it will still contain some minerals. You can expect less scale buildup using filtered water, but it will still occur, especially over time.

How effective filters are against pathogens varies greatly based on the brand used. Some are highly effective against bacteria and single-celled organisms, while others are likely to let smaller pathogens slip through. All filters seem to struggle to some degree with viruses, which are often too small to capture.

While filtered water is likely to contain fewer minerals and pathogens than tap, some will still be present. For this reason, distilled water is a much better bet than filtered for your humidifier.

Note: The best filter to use is a reverse osmosis water filter.

Can You Use Bottled Water In a Humidifier?

woman pouring water

Bottled water, or spring water, is likely to contain fewer chemicals, such as chlorine, than tap water. However, the mineral and pathogen content is frequently on par with that of tap water.

Even brands like Aquafina, which puts its water through additional purification steps before bottling, are not as pure as distilled water.

The fact is that humans need minerals in their drinking water to stay healthy. This is one reason most types of drinking water are not purified to the standards of distilled water. And one very good reason not to use spring or bottled water in your humidifier.

Of course, if your choices are bottled water or tap water, bottled water is the better choice. But you should only use this type of water for limited periods.

Can You Use Tap Water In a Humidifier?

a person getting tap water

As you can probably guess by now, it is not recommended to put tap water in your humidifier. 

The biggest problem has to do with the mineral content of tap water. The minerals in your faucet water are aerosolized at a rate of around 85 to 90% in an ultrasonic humidifier. That means that most of the calcium, magnesium, nitrates, and chloride in your water end up in the air, where they can be breathed in.

Worst, most tap water contains trace amounts of heavy metals like lead. These substances pose an especially high risk to children whose brains are still developing.

Using a demineralization cartridge can help remove minerals from the water if tap water is your only option. These can be very helpful in preventing scale, but they won’t remove all minerals from the water or mist. 

Note: In addition to minerals, tap water is also likely to contain an array of pathogens, including mold, bacteria, and viruses. When these get forced into the air, they are more likely to be inhaled and cause illness. 

If your reason for using a humidifier is to help relieve respiratory symptoms from an infection, you could actually be doing more damage by introducing secondary infections.

While bottled and boiled water are not perfect, both are better than tap water. But, the best water for a humidifier is, hands-down, distilled water.

Should You Put Hot Or Cold Water In a Humidifier?

For the most common type of humidifier—ultrasonic—room temperature distilled water is your best choice. This temperature optimizes the unit’s output efficiency, thereby conserving energy.

Cold water is your best bet if you’re still using tap water for your humidifier. Hot water has more dissolved minerals, leading to more scale build-up and more aerosolized minerals. On the other hand, warm water is more likely to breed mold and bacteria than cold water. Though, the water will likely warm to room temperature before it is all consumed, which may undo some of the beneficial effects of cold tap water.

If you have a steam-based humidifier, adding hot water to the reservoir can help save energy. If you add cold, the unit will need to work harder to heat the water to boiling before it can produce steam.

Note: Evaporative humidifiers also work best with room temperature distilled water. If you use tap water, cold is less likely to contain as many minerals. But, it is recommended to let the cold water warm to room temperature before adding it.

How Do You Get Rid of Scale In a Humidifier?

a bottle of white vinegar

If you’ve been using tap water in your humidifier, you’re likely dealing with scale build-up. It’s important that you work to get rid of this white residue every time you clean your unit since scale can harbor and contribute to the growth of bacteria and mold.

Although many commercial products can eliminate limescale, the cheapest and safest is likely already something you have in your home.

Scale is a build-up of alkaline minerals. The easiest way to denature them is to add a liquid acid to the mix. For a humidifier, the safest thing to use is distilled white vinegar. It will also kill any mold and bacteria that have grown.

  1. Simply pour white vinegar into the tray of your unplugged humidifier
  2. Allow it to sit for five minutes. 
  3. Then, scrub away the scale with a brush.
  4. Rinse away the vinegar, then scrub the surface with warm soapy water to remove any remaining pathogens. 
  5. Rinse thoroughly. Then, your humidifier will be ready for use again.

Investing in a humidifier that is easy to clean, such as the Okaysou Aqua Q6, is important. While scale won’t be a problem if you use distilled water, regular cleaning is still essential to keep mold and bacteria introduced from the environment at bay.

About The Author

Sara Seitz is a freelance writer and novelist. She lives with her husband and wildling toddler in Colorado where she spends her days working on their house, gardening, and reconnecting with nature.

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