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What Kind of Water Should You Use in a Humidifier?

by Mark Timmons & Zileni Milupi July 09, 2024 0 Comments


Humidifiers have swiftly emerged as a crucial element in various regions across the country, particularly in drier climates. They're frequently employed during winter to counteract the loss of moisture caused by heating systems. Despite their widespread use and functional importance, the water used in humidifiers often goes overlooked.

Selecting the appropriate water for your humidifier is a critical factor that impacts its efficiency and the air quality within your home. In this guide, we'll delve into the various types of water and their effects on humidifiers. There are basically two types of humidifiers: Room Humidifiers and Whole-House Humidifiers. Of course, there are large commercial humidifiers that are used in a variety of businesses and industries, such as libraries, labs, humidors, and others.

The type of water you should use with a humidifier depends on the type of humidifier you have and your local water quality. If you have a humidifier with a built-in filter or if you regularly clean and maintain your humidifier according to the manufacturer's instructions, you may be able to use tap water safely. Keep in mind that tap water varies in quality depending on where you live, so if your tap water is particularly hard or has a high mineral content. It's always a good idea to check the user manual for your specific humidifier model for recommendations on the type of water to use.

Let’s look at the types of water that you might want to consider using in your humidifier:

 Tap Water

Although tap water is convenient for many people, it often contains minerals like calcium, magnesium, and other impurities. When used in a humidifier, these minerals can create mineral deposits, which lead to reduced efficiency and potential damage to the humidifier's components. The minerals and chemicals can additionally be released into the air, contributing to indoor air pollution and potentially causing or worsening respiratory problems. While tap water might not seem like the best option, it does have some benefits worth noting:
  1. Tap water is readily available from faucets in homes and requires no additional effort or cost, making it a convenient option for refilling humidifier reservoirs.
  2. Tap water is more affordable and does not require special purchasing or filtration equipment. This makes it a cost-effective choice for homeowners looking to save money on humidifier maintenance.

The trade-off is that if your water is moderately or highly mineralized, the system's life will be dramatically impacted. Limescale can quickly destroy a great product.  

Distilled Water

Distilled water is purified through boiling and condensation, which removes impurities and minerals. This prevents mineral buildup or "white dust" residue that can accumulate in the humidifier and be disrupted into the air. This residue can settle on surfaces in your home and even worsen respiratory issues in sensitive individuals. Therefore, the use of distilled water in your humidifier will massively improve the quality of air. 

Using distilled water can also extend the lifespan of your humidifier and reduce the frequency of maintenance and cleaning. Since distilled water does not leave behind mineral deposits or residue, there is less risk of clogging or damaging the humidifier's components. This can save you time and money on repairs or replacements in the long run. The humidifier will be free of limescale buildup, efficiency will be dramatically improved and overall operation will improve. Distilled water is very expensive to make or buy due to the energy cost involved. You can purchase a gallon of distilled water for $1.25 to $1,50. If you have a room humidifier, this may be affordable short term, but the cost is prohibitive for whole-house humidifiers.

Reverse Osmosis Water 

Reverse osmosis (often called “RO” water) is a water purification process that utilizes a semi-permeable membrane to remove impurities and contaminants from water. Here's a description of the steps involved in the reverse osmosis process:
1. Pre-filtration: Before entering the reverse osmosis membrane, water typically goes through pre-filtration stages to remove larger particles, sediment, chlorine, and other substances that could damage or clog the membrane. This step helps prolong the membrane life and enhance the system's efficiency.
2. Pressurization: The pre-filtered water can be pressurized using line pressure and a bladder tank or a pump to push it through the reverse osmosis membrane. The pressure applied is typically higher than the osmotic pressure of the water, which is the force required to prevent solvent flow across a semipermeable membrane to a more concentrated solution.
3. Separation: As the pressurized water passes through the semi-permeable membrane, the membrane allows only the solvent molecules (usually water) to pass through while blocking the passage of larger molecules, ions, and contaminants. This separation process effectively removes impurities such as salts, minerals, heavy metals, bacteria, viruses, and other pollutants from the water.
4. Product and Reject Streams: Permeate or product water is purified water that successfully passes the membrane. Simultaneously, the concentrated stream containing the rejected contaminants is called the reject or brine stream. The reject stream and removed contaminants are typically discharged or directed to a drain.
5. Post-treatment: In some reverse osmosis systems, the purified water may undergo additional post-treatment processes to further enhance its quality. This may include remineralization to improve taste and pH adjustment to achieve desired levels.
6. Storage and Distribution: The purified water is then stored in a storage tank before being distributed for various applications, such as drinking, cooking, or industrial processes.
Reverse osmosis removes a wide range of contaminants through a physical separation process, making it an effective method for producing clean, purified water. It is commonly used in residential, commercial, and industrial settings to provide safe and high-quality drinking water in residential, commercial and industrial settings. In actual application, the cost can be as low as $.02 per gallon.


Deionized Water

Deionized water (or DI Water) may not be the most practical or cost-effective choice for everyday use in a humidifier. Deionized water has had its mineral ions removed through deionization, which typically involves passing water through ion exchange resins or other methods. Using deionized water in a humidifier can help reduce mineral buildup and scale formation, similar to distilled water. However, deionized water may be more expensive and less readily available than distilled water, depending on your location and access to water treatment facilities. Depending upon your water’s level of mineralization, DI water can cost $.25 to $.60  per gallon to make.  However, if you use reverse osmosis ahead of deionized cartridges, the cost drops to as low as $.02 - $.03 per gallon.

Filtered Water

Filtered water is somewhat better than tap water because it does removes solids and or chemicals, but it does not remove the minerals from the water, so while the chemicals in the water may be removed and not atomize into the air, the minerals in the water can wreck havoc on the humidifier itself. If you are in an area where the water is highly mineralized, this is really not an option.

Softened Water

Ultimately, whether soft water is good for your humidifier depends on your specific circumstances, including the type of humidifier you have, your water quality, and any personal preferences or concerns you may have. If you're unsure, you can consult the humidifier's user manual or contact the manufacturer for guidance on the best type of water to use.

However, it is less likely to cause mineral buildup and scale inside the humidifier. This can help prolong the life of the humidifier and reduce the frequency of cleaning. Softened water is often treated using ion exchange resin systems that replace calcium and magnesium ions with sodium ions. While this makes the water softer, it can also increase its sodium content. If you have concerns about sodium in the air and white sodium dust on surfaces, you may want to consider not using softened water or use another type of water, such as distilled water or RO water.

Regular Filter Replacement

To maintain the quality of filtered water, it's crucial to replace the filters in your filtration system regularly. Over time, filters can become clogged with contaminants, reducing their effectiveness at removing impurities from the water. Regular filter replacement ensures that your filtered water remains clean and suitable for humidifier use.

Monitoring Mineral Buildup

While filtered water contains fewer minerals than tap water, some mineral content may still be present. It's important to monitor your humidifier regularly for signs of mineral buildup and perform maintenance as needed to prevent clogging and maintain optimal performance.


In conclusion, the significance of selecting the appropriate water for your humidifier cannot be overstated. As humidifiers become increasingly essential in countering dry climates, understanding the impact of water types on efficiency and air quality within your home is paramount. Tap water, while convenient, can lead to mineral deposits and indoor air pollution, potentially affecting respiratory health and humidifier longevity. 

Distilled water offers a purified alternative, reducing mineral buildup and improving air quality but comes at a higher cost. Reverse osmosis water, although initially more expensive to set up, provides a cost-effective solution in the long run, effectively removing impurities and contaminants. 

Deionized water and softened water present additional options, each with its considerations and potential drawbacks. Regular maintenance and monitoring of mineral buildup are crucial regardless of the water type chosen, ensuring optimal performance and air quality. Ultimately, the choice of water for your humidifier should be informed by factors such as water quality, humidifier type, and personal preferences, with careful consideration given to the long-term effects on both the appliance and indoor air quality.
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