Here's an unexpected source of water for the garden: An air conditioner's condensation pipe.
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There's another source of free water that many of us don't even consider: the water from an air conditioner's condensation pipe. You can use this water to irrigate small plants and vegetable nearby. The small drip of water will keep the plants moist all summer.
No matter what kind of air conditioner you have, whole house or window box, it drains water that you can capture. Each time an air conditioner runs, it pulls moisture from the air inside the home. Since the water has to go somewhere, it's drained outside the house, usually through a condensation pipe. The water slowly drips from the pipe each day. It doesn't seem like a lot of water, but the constant dripping really adds over time. This water can be caught in a bucket or fed directly to nearby plants.
Using the air conditioner water can be an extremely efficient way to take care of nearby plants. Choose plants that get only a few feet tall so they won't grow over the unit. You can plant small vegetables near the end of the condensation tube, and they'll get constant water over the summer when air conditioner runs more often.