When I have to run the hot water before starting the dishwasher I usually catch it in a pitcher and use it to water the plants and that got me wondering.
Not because of the temperature but because the hot water has more dissolved minerals in it (yes I am aware this means my tank probably needs flushed; it’s on the better half’s honey-do list).
I guess now I am curious if water closer to room temperature is better for them too since it would be less of a shock.
There are very few plants that would see any measurable benefit from the dissolved minerals in tap water. Dissolved minerals are actually to some plants’ detriment, because they tend to make water more alkaline. House plants are often tropical plants that evolved in humid, rainy areas with acidic soils. Watering with rainwater or distilled water and using an appropriate fertilizer are almost always going to yield a better outcome.
Temperature-wise, room temperature is best. Plants don’t expect or like hot water
If your house has lead soldered pipes that could be an issue. Many (most?) plants tolerate lead well, I wouldn’t want to use it on my tomatoes though. Radon could also be a problem for indoor air quality.
As far as temperature goes plants wouldn’t be exposed to temps above body temperature, even in a hot climate rain is going to be well below that. In my experience seedlings especially do not like warmer water, when I use it I water around the plant and not at its base.
Whether your plants can benefit from increased minerals is going to depend on the plants needs, the soil mineral content, and the mineral content of your water.
