I have been to the Kortright Centre north of Toronto where water is recycled, and being the child of depression era immigrants, finiteness of resources was something I learned with gardening.
I bought a mid-efficiency furnace last year, and the water drip line is directed into a basement sink. I am surprised at how much water is extracted during the air conditioning season, since I must have measured one litre of water extracted per hour one afternoon.
I wonder if that water has any nutritious use left, such as for houseplants.
The reason I ask, is that it had been expelled in the front garden in the past, but the location was changed for aesthetic value, and now I was thinking of doing some indoor gardening long term and using that water, but have reservations not knowing how it could affect plants, although I do not have vegetables.
Thank you for contacting the Toronto Master Gardeners with this interesting question. I applaud you in wanting to preserve one of our precious resources. The answer to this question is not a clear yes or no answer.
AC and dehumidifiers work in a similar fashion. Both reduce excessive humidity by refrigerating metal pipes. When exposed to humid air, the coolness of the pipes causes the water to condense. In the case of the dehumidifier the water pulled from the air, called condensate, flows into a bucket, that must be emptied periodically. In the case of the AC the condensate is drained either outdoors or in the case of a high efficiency furnace directly into the drain in the basement floor. When temperatures are high the amount of condensate can range anywhere from 23-91L of water per day.
The condensate pulled from the air can contain bacteria, fungi and other microorganisms that can build up in the pipes. Likewise it may contain trace metals leaching from the metal parts of the condenser. For this reason it is not recommended that you use the runoff on edible plants. According to the Laidback Gardener “ That said, dehumidifier and air conditioner condensate is not so contaminated that it can not be used for other purposes. It is considered to be “gray water”: water that insufficiently pure for human consumption, but that doesn’t require any special treatment to be used for other purposes.”
Unlike your tap water, the AC water contains no chlorine or other minerals that plants can use for their growth. It is essentially distilled water. You can use it to water plants that don’t tolerate mineralized water, such as carnivorous plants, as well as plants that react badly to the chlorine found in tap water, such as dracaenas (Dracaena spp.), marantas (Maranta spp.) and spider plants (Chlorophytum comosum). If you would like to use the AC water for your plants then mixing it with rainwater should help balance the amount of minerals and keep your plants happy.
Lastly, air conditioning water is also extremely cold straight out of the tubing and can affect plants if applied directly. Let the water come to room temperature before using it on your plants.