Gary, you say that "But plants do not particularly like chlorinated water". Other than anecdotal "evidence", can you provide some scientific evidence. This might be helpful: https://www.gardenmyths.com/chlorine-chloramine-plants/

I have an extensive dripper system that supplies water to almost all of my plants, including my figs, my vegetable gardens, my bamboo, my various fruit trees, my shrubs and ornamentals, and many potted plants. They all do well with my chlorinated city water. The chlorine content is about 1 ppm, and the EPA standard is no more than 4 ppm. These levels are far below the levels one would fret about as having an impact on plants.

Vladimir, I am not a research scientist. OP asked my opinion and I gave it. Your link does tend to support my opinion that plants do not particularly like chlorine, can even be toxic at higher levels. I doubt there is a good statistically valid study on whether tap water or rain water is better for plants, just too expensive. But it would seem to me that rain water would contain less contaminants than tap water and would be better for plant growth, provided adequate nutrients were added. But just my opinion.

Gary- Lots of things can hurt or kill plants and humans in too high doses, but are harmless or even beneficial at lower concentrations. I‘ve read nothing that suggests the minerals or chemicals in ordinary tap water that passes regulatory standards — and specifically chlorine — can pose a threat to plant growth.

I asked because it stands to reason that chlorine could be less than ideal for plants. I say that because chlorine is added to waters systems as an antibacterial agent. I've read that plants do best when they are grown in soils with high concentrations of beneficial bacteria that break down organic matter in the soil into nutritious compounds the plant can use. The less bacteria (presumably because the chlorine killed some of it) the less nutrition will be available for the plant. I also know most gardeners use tap water to for their plants when rain is insufficient. As an experiment, I'm going to set out a rain barrel to collect rain and try using that for the rest of the season. I’ll let y’all know how it goes.

Gred- I’m sure that rain water will be as good as anything for your plants, but I’m skeptical whether it will show any difference. It’s an interesting experiment, though, and it will be informative to hear your results, so please report back. Have fun :-)

It makes sense that rain water is preferred over tap or well water. The plants evolved on rain water. One thing that hasnt been mentioned is ph. Rain water has a lower ph than well (passing through limestone) or tap (ph artificially raised to keep pipes from corroding). Studies have shown how ph levels can effect nutrient uptake.

Kevin- A pH scale goes from 0 to 14, with 7 being neutral; as values go lower than 7, it means increasing acidity; higher values refer to increasing alkalinity. Rain water should be close to neutral. In general, plants don’t want extremely acidic or extremely alkaline pH values. However, some plants prefer somewhat acidic soil, while others prefer somewhat alkaline; and some prefer neutral. So it’s important to recognize relative values when we talk about “low“ pH values.

I still think it has more to do with the atmospheric conditions that you get greater growth than the actual difference between tap, well, or rainwater. I know tomatoes split because tomatoes grow faster than the skins. This can happen when the weather cools off and it looks like it is going to rain but does not. I have also noticed that if we get a heat shower in which it rains and heats back up in less than an hour the plants do not respond with growth as well as when it rains and stays cool for a few hours. No research, just things that I have noticed,

I would use a complete fertilizer such as miracle gro at a rate of 1/2 teaspoons per gallon at each watering and see how the figs react. I have gotten good growth from figs doing that using tap water.

There are so many things that factor into plant grown and production, but my amateur observations lead me to believe that rain water is best, but also it does more than hydrate the plants. All my outdoor plants, figs included, whether potted or inground react to a good rain storm with near explosive growth. That is, provided of course they aren't left in standing water. The weather patterns here just seem so out of wack now because we only get a good soaking summer rain once every other week. In between the temps are in the 90's. Oh well.