I have always used our house tap water to water my trees. It is alkaline, about 7.5 to 8, and very hard, GH 180 and KH 240. The worst problem it has caused that I am aware of is lots of scale on pots and sometimes leaves.
Now I have a couple of nice trees that prefer acid soil and softer water. I can take care of the Ph by adding acid to the water. That is what I do with hydroponics. But all the solutions to hard water (softners and RO) are not something I want to use.
Rainwater seems to be the best DYI solution. It tends toward neutral/acidic and is not hard. That works in the summer time where it is easy to collect and use. Somehow I am not there to collect snow and ice melt in the winter. But I guess I could. The only downside I see is; I have raccoons around the house. Sometimes they go on the roof so I would have raccoon poop soup. And no, killing off the raccoons is not an option.
I could buy distilled water but the ones I have measured would need the Ph lowered.
Thoughts? Lessons learned?