Is dehumidifier water safe to use on plants?
Experts weigh in
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During dry summers, when many areas are experiencing droughts or watering bans, people start looking for ways to use less water. If you have a dehumidifier, you’ve noticed that the dehumidifier has a reservoir that fills up with the water.
Instead of pouring that dehumidifier water down the drain, you may be able to use it water the plants on your windowsill, deck, or patio instead of having to turn on the garden hose or break out the watering can. However, should you really use dehumidifier water for plants?
We spoke to experts to get the scoop on using dehumidifier water for plants at home. Here's what they had to say.
What’s in dehumidifier water?
Dehumidifiers work by cooling the air in your room so water condenses out of the air and into the dehumidifier’s water reservoir. The dehumidifier then passes the air over warm coils before blowing it back into the room.
This process (cooling moist air until water condenses out) is how we get rain. It’s not distillation, which involves boiling water, and makes water safe to drink. The water isn’t boiled, so any bacteria, mold, or dust that was in the air or sitting on the fan will be in the water when it gets to the humidifier reservoir.
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Unfortunately, most people don’t look into their dehumidifier reservoirs, much less clean them, and don’t empty the dehumidifier reservoir unless they have to, which means that mold and microorganism can grow for a long time in a dehumidifier reservoir.
That possible contamination makes dehumidifier water a type of gray water, a term for water that has been “used” for some purpose, like washing dishes or showering, but doesn’t contain sewage. Some worry that heavy metals from the cooling coil might get absorbed into the dehumidifier water. Others say that the amount of copper, zinc, and aluminum in a dehumidifier’s water reservoir is minimal.
That said, dehumidifier water isn’t filtered or treated after it comes off of the dehumidifier coils. If there is heavy metal contamination, it’s not coming out—and you won’t know if it’s there unless you pay for a laboratory test. Still, contamination by mold and microorganisms is much more likely.
Is dehumidifier water for plants a good idea?
Whether water from a dehumidifier is good for plants or not depends on what plants you’re talking about. Water from a dehumidifier is good for watering plants outside your home during a drought. And since about 30% of drinkable water in the U.S. is used to irrigate outdoor plants, during a drought it’s a good idea to use any gray water you can for watering your yard.
When it comes to indoor plants, you can use water from a dehumidifier to give your thirsty houseplants a drink.
That said, you probably shouldn’t use dehumidifier water for plants you are growing for food because of the possibility of contamination by mold, bacteria, and other microorganisms.
This goes double for plants you intend to eat raw like microgreens, salad greens, fresh herbs like basil and cilantro, and container-grown tomatoes. If you wouldn’t drink it (and you shouldn’t drink dehumidifier water), you shouldn’t use it on edible plants.
If you’d like to know more about how to use dehumidifier water, shower water, and other “used” water for outdoor irrigation, the U.S. Environmental Protection Agency has guidelines for using gray water for watering outdoor plants.
Remember, dehumidifier water isn't cheap.
“Your electric dehumidifier at home ‘produces’ very expensive water,” said Omar Yaghi, James and Neeltje Tretter chair in chemistry at UC Berkeley. If you’re running a dehumidifier anyway, go ahead and use the water for your plants, but just don’t think you’re really saving any money on your water bill.
Prices were accurate at the time this article was published but may change over time.