White dust, minerals, and what water to use

Why tap water can leave white dust, and what the EPA suggests.

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What white dust is

The EPA says ultrasonic and impeller humidifiers "are very efficient at dispersing minerals in tap water into the air," and that some people notice a "white dust" on surfaces.

What the EPA suggests

The EPA says to "Use water with low mineral content, such as distilled water, to prevent releasing minerals into the air." It also says distilled water "still contains some mineral content," but likely less than most tap water.

Reading the bottle

The EPA says bottled waters labeled "spring", "artesian" or "mineral" have not been treated to remove mineral content. It says distillation is the most effective method for removing minerals.

Scale in the tank

The EPA says minerals in tap water may increase crusty deposits, or scale, inside humidifiers. Our cleaning guide covers how often to remove it.

Cartridges and filters

The EPA says the ability of demineralization cartridges, cassettes, or filters to remove minerals "may vary widely." It says to watch for white dust as a sign that minerals are not being removed.

This is general information, not medical or purchasing advice.

Sources: EPA, Use and Care of Home Humidifiers.

FAQ

Do evaporative humidifiers make white dust?

The EPA says steam vaporizer and evaporative humidifiers "are not expected to disperse substantial amounts of minerals."

Is purified water the same as distilled?

Not always. The EPA says "purified" water may be produced by distillation or by other processes that are generally less effective at removing minerals.

How to clean a humidifier, per the EPA

Daily water, regular cleaning.

Cool mist, warm mist, ultrasonic, and evaporative humidifiers

Four types, in EPA terms.

Humidifier filters and running costs

Filters, water, and power.

Next: cleaning