Is Air Conditioner Water Safe for Plants?


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With conservation on the rise around the world, many people are looking for ways to help conserve natural resources. Plants are crucial to sustaining biodiversity on our planet and need adequate water, just as humans do. Balancing sustainability and need can be complex but can certainly be achieved by recycling water for plant irrigation. For this purpose, is air conditioner water safe for plants?

Air conditioner water is formed by condensation of the outdoor air filtered into a unit’s cooling system. This water is generally safe for plants, but since the water is distilled, a lack of nutrients may not give plants adequate nutrition. Bacterial growth is also a concern with A/C water. 

Unlike humans and animals, plants do not have picky internal systems when it comes to water quality. However, there are both positive and negative outcomes of using air conditioner water for watering your plants. Nutrients, water quality, and water cleanliness are all important factors to consider. Read on to find out more about the safety of air conditioner water for plants.

How Is Air Conditioner Water Different From Regular Water?

I grew up in the sub-tropics of the Southeastern United States, and I realize that not everybody is as well-versed in air conditioner mechanics like those of us from the south. But it is totally normal to wonder if the water coming out of an air conditioner is toxic to plants and the foliage surrounding a unit. 

Air conditioner water is what is known as distilled water. This type of water can be understood as lacking the essential minerals that are commonly found in drinking water. For plants, this can pose some problems since crucial minerals will be missing, yet plants will still receive proper hydration. 

Regular water can mean tap water, spring water, or any type of water that still has proper mineralization. Without a doubt, optimal plant growth will respond more positively to mineralized water as opposed to distilled water. Let’s look at some of the ways that air conditioner water is not ideal for plants in more detail. 

How Is Air Conditioner Water Detrimental to Plants?

Air conditioner water is a great way to support conservation through the limitation of wastewater. Because air conditioner water is simply the excess vapor from dehumidified outdoor air, the liquid is not considered toxic. You do not have to worry about freon or any other air conditioner chemical mixing with this drain water. 

On the other hand, this water does cross over copper pipes that form the cooling pipes in an air conditioner. This may sound alarming, yet no evidence suggests this causes contamination. The two big downsides of using air conditioner water for plants is the lack of essential nutrients and the possible growth of bacteria in the unit. 

Lack of Nutrients

As previously mentioned, the water from a cooling unit is distilled; the outdoor moisture in the air is turned into vapor. The cooling components of the unit condense the vapor back into a liquid. This may sound clean and beneficial, but nutrients that plants need are lost because the water is not mixing with the other elements of the Earth. 

Plants need minerals for photosynthesis to take place properly. With tap water, they will get these minerals, yet tap water is also not ideal because it contains an overabundance of minerals and chlorine. But distilled water from an air conditioner doesn’t have enough, so where is the middle ground? 

A great solution to this would be to use air conditioner water with a fertilizer of your choice. With this solution, your plants can have pure water without harmful tap water additives and have proper nutrients from the fertilizer. Even with the fertilizer solution, there can still be some problems with possible bacterial growth in air conditioner water. 

Bacterial Growth

If you have a window unit, there is probably a small hole at the bottom of the unit that allows drain water to continuously drain out. This is great because it prevents the possibility of the water backing up into the unit and, worse, lying dormant, causing bacterial growth. Stagnant water is a breeding ground for bacteria and some types of insects, like mosquitoes. 

This applies if you allow the water to collect in the drainage tray and then use it for plant irrigation or if you allow the water to collect in buckets over time. Plants are more resilient to bacteria than animals, yet an overabundance of bacteria may harm plants. 

An even bigger problem with bacteria in stagnant a/c water is when it is used for indoor plants. You are allowing harmful bacteria and pathogens to grow inside your home, which can be hazardous to your health. Therefore, it is important to never allow air conditioner water to remain dormant.

With this in mind, how exactly do plants respond to air conditioner water?

How Do Plants Respond to Air Conditioner Water?

There is a universal truth when it comes to water: all living things require at least some amounts of it. Apart from saltwater or heavily diluted water, most plants will happily absorb water to survive. With this said, some preferred types of water adequately support plant health. 

Furthermore, there are also some differences between how common outdoor plants respond to water type vs. potted indoor plants. 

Outdoor Plants

Distilled water is in many ways similar to rainwater. Since most outdoor plants and foliage do not have humans to conveniently supply water, rainwater is the main source of plant water. This may sound contradictory to the argument against distilled water, but outdoor plants can absorb all the minerals transported by rainwater through their root systems. 

So while rainwater may not be ideal in and of itself, the minerals are replaced through soil pickup. Therefore, if you have plants underneath a window air conditioner or near an outdoor unit, the distilled water will mix with the soil, and no nutrients will be lost. There could be a problem with too much water if the unit is constantly dripping water onto plants or grass, so be mindful of that.  

Potted Plants

Using air conditioner water for potted plants or plants that are grown indoors may not be totally safe. Unlike outdoor plants, indoor plants do not have the benefit of having the surrounding outdoor environment to make up for the mineral loss. 

Potted plants already have less soil distribution than outdoor plants. For this reason, the air conditioner water will only satisfy basic hydration for indoor plants. You could consider using something like Miracle-Gro as an add-in with the air conditioner water to replace the essential nutrients. 

As a result, air conditioner water or any type of distilled water will effectively hydrate plants. The mineral loss is not severe for outdoor plants, yet there may be some problems with indoor plants. 

Final Thoughts

To conclude, air conditioner water is okay for plants. However, not the optimal type of water to support healthy plant growth. It is a great way to do your part with water conservation, and your plants won’t mind air conditioner water in the short term. It is not recommended to give your plants air conditioner water that has sat stagnant in a unit’s drain pan; this promotes bacterial growth. 

If you are worried about the grass surrounding an outdoor unit, the effects of air conditioner water are better tolerated with outdoor foliage. Consider fertilizer for indoor plants.

Chris Hewitt

Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

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