Can You Use Soft Water In A Humidifier? [Reasons Explained]

When it comes to using a humidifier, people are often concerned about what type of water they should fill in the tank. There are so many choices that it is hard to identify between each other.

Many friends have asked me if they can use soft water in a humidifier, so I decide to write this post to answer this question.

Yes, you can use soft water in a humidifier. It contains fewer minerals than tap water, making your humidifier not so prone to white dust, clogs, and germ growth as before. However, distilled water is still a better choice than soft water.

In this post, I will explore what soft water is, how to get soft water at home, and a set of pros and cons of using soft water in a humidifier. Keep reading, and you will get a lot of helpful information.

What is soft water?

what is soft water

In the US, water is classified by its hardness which is the amount of dissolved calcium and magnesium in the water.

Water that contains 0 to 60 mg/L (milligrams per liter) of calcium carbonate is classified as soft, while 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard.

A study has shown that water in many areas in America is hard or even very hard, so it is hard for people in these areas to get natural soft water from the pipe.

Difference between soft and softened water

Since tap water in many regions is relatively hard, people who want to use soft water should take measures. 

Softened water is the water that has been transformed from hard water by means of a water softener system. It is a type of soft water but has to get through a specific process.

Water in some areas is naturally soft, and the rainwater before hitting the ground is also soft water.

Benefits of using soft water in a humidifier

While soft water is not the best choice for humidifiers, it is much better than tap water. No matter the source of soft water, it contains less calcium carbonate and magnetism carbonate. 

As you know, the dissolved mineral will settle down and become mineral buildup in the humidifier water tank. These scaling and lime are hard to remove, extending your time on cleaning the machine. It could turn white dust, which will land on the furniture’s surface.

In addition, mineral deposits could be the nutrition source of mold spores, bacteria, or other microorganisms. It can pose health hazards to you when you inhale the air. 

Beyond that, mineral buildup can clog the machine gradually, shortening its lifespan.

By filling your humidifier with soft water, these adverse effects caused by mineral deposits will be vastly reduced.

Moreover, soft water contains a certain amount of salt, which can increase the efficiency of vaporizers.

Disadvantages of using soft water in a humidifier

Even though soft water is beneficial for humidifiers in many ways, it still has some drawbacks, making it not the water recommended by manufacturers. 

Salt in the water

salt in soft water

Most water softener tablets and systems work by replacing calcium and magnesium with sodium and potassium, known as ion exchange resin.

Therefore more sodium and potassium will get into the water, although the amount is minimal. That’s also why some people feel their softened water is salty.

Salt can help with vaporizers, but it may corrode the parts in humidifiers, shortening the device’s lifetime. 

Residue in the water

There are various dissolved minerals and germs in tap water. While water softener systems can remove calcium and magnesium, they don’t filter out other substances. 

It means that there would be some mineral build-up in the water tank over time. The residue will also become the nutrition source for mold and bacteria.

Water softener system cost

water softener system

For those people who don’t live in an area with soft tap water, you need to install a water softener system or use softener tablets.

On average, a water softener system will cost you about $1500, which could be a lot of money for some people. Softener tablets are much cheaper, but you have to treat the water a few times a day, which is a tedious task to do.

If you are unsure about the hardness of water, you can buy a water hardness test kit to decide which type of softener system you need.

Why is distilled water still better than soft water?

Again, you can use soft water in a humidifier. After all, many people add tap water to a humidifier without causing too many issues, and soft water is better than tap water.

But distilled water is still the best choice because it doesn’t contain any minerals and other impurities at all.

Compared to distilled water, soft water still contains minerals, bacteria, and mold. The salt is also possible to rust the parts and accessories. So you will spend more time cleaning it, and the lifespan would be shorter than if you used distilled water.

See also:

What type of water you can add to a humidifier?


Soft water is better than hard water in many aspects, and the same is true for humidifiers. It comes with less calcium and magnesium, meaning fewer mineral build-ups will form in the humidifier tank. 

Tap water in many regions is not soft, and you should install a water softener system or use softener tablets to get soft water. 

However, other impurities are not removed at the same time, making it less ideal than distilled water for humidifiers. Other than that,  more salt will enter the water after the reaction with calcium and magnesium, which may corrode the machine, leading to rust and clog in the long term.               

About The Author

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested dozens of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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