Late last summer we tested capturing the condensate that is pumped out of our central AC unit, and found it produced ~14 gallons per day when it's hot/humid out. That would go a decent way towards filing our plant watering needs.

However, I've read that AC condensate can be slightly acidic, and maybe not the best for all types of plants. Is there an easy way to treat the water with something that would make it better for general watering?

Garden lime seemed like it would be worth asking about in particular, but not sure if it would be able to treat water like that. If so, any idea how much lime to use per gallon, and how to prepare? If lime couldn't be used, any other ideas?

I should add that many of our plants are in containers or in a raised bed on our back deck. So having the water be appropriate for container irrigation is important, if that's a consideration.

2 Answers 2


It is essentially pure water but has absorbed gases from air . The only gas that has an affect in this situation is CO2. It dissolves and makes carbonic acid, I forget the pH, it may be about 4.

The acidic nature of the water makes little difference to plants if they are in soil. The buffering affect of soil, particularly calcium, overwhelms the tiny quantity of acid. I often use rainwater, I think the main advantage is that it does not add calcium and other hard water elements that are usually in tap water.

The pH is a measure of intensity (like voltage), not a measure of quantity (like amperage). You could measure the pH of your soil, if interested. Get aquarium pH test solution (used to be $.49, I am sure it is more now). Take a spoonful of soil, add a couple spoonful's of clean water, shake, let settle, do the pH test on the water.

  • Thanks. Ha ha, so now I went out to try to connect a tube to the outlet of the condensate tubing, and it's so brittle from sitting in the sun for so many years. I'll have to get creative on how to capture this water, but thanks for the info.
    – Emily Beth
    May 24, 2021 at 18:59

During the hot summers, I put water tanks under the end of the AC water runoff pipes of the building. Most of the water is otherwise wasted, and I save lots of water when I irrigate.

Recently, I've been (in the last two years) into tropical plants, a dramatic shift from strictly succulents and fruit garden. I still tend my succulents and fruit trees, and just added extra activity in the form of tropical plants. My plants include Aroids, Begonias, Hoyas, Calatheas and Maranthas.

There are cons and pros for AC water, depending on your usage.

The main "con" of AC water is lack of nutrients, but this can be compensated by adding nutrients periodically as compost or adding them into the water, so this is not a problem. I don't think AC acidity is a concern, because it is the same as rain water in this regard. In addition to AC water, I have the waste water coming out from an osmosis filter. My brother uses the filter to prepare pure water needed for his sea-water aquarium. The municipal water, going through steel pipes, ends-up with a high conductivity, and you cannot just add sea-salt and put the corals in. Each time he refreshes some of the water, he runs the filter and stores clean water to which he later adds salt. This waste-water is not wasted, and is stored in a tank which is later used in the garden. This has more nutrients than the average municipal water (all "contaminants" are more concentrated) and can make-up for the lack of calcium and low pH.

The pro of AC water: They lack salts and other chemicals which may accumulate in the soil, especially if you don't flush enough when you water. This is essential, and even crucial, for many of my tropical plants, and Calatheas in particular would have otherwise ended with brown patches all over.

My advice is use it. If your plants love a higher pH then adjust it with calcium or other additives available in hydroponic stores. In hot days they even supply water for all my plants and the garden.

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