What about out door growers & rain water along with all those atmospheric pollutions which your plants may asborb & by the act of inhaling.... you take in !
The questions on the pH of rainwater was something I looked up several years ago out of curiosity. The usual pH of rain water is 5.0 to 5.5 according to the US EPA. The pH is influenced by the carbon dioxide and other naturally occurring compounds that can be in the atmosphere which will form acids as they mix with the water in the air.
The acid rain issue that came up in the 1980s is rarely mentioned any more and I figure that as more factories, power plants and other sources of air pollution installed scrubbers in their smoke stacks or switched over to other fuels which are cleaner burning. Who wants a coal burning power plant in their neighborhood when natural gas can be used.
With the average rain being a bit on the acid side we can look at what happens when it falls. We know that some of the elements, micro-organisms and organic materials in the soil will slowly change the pH of the water as it moves through the soil so the acid is gone and by the time the water enters the aquifers it is closer to a neutral pH. However, the water can pick up dissolved minerals in the soils, sands and stone and it becomes alkaline and be called hard and have a higher pH.
The pollutants in the atmosphere that you mention are not as big of a problem now as they were 100 or 75 or even 50 years ago. Yes, they are still there but the amounts have been dropping steadily. Same with the water in rivers and lakes. The levels of pollutants are lower now than they were years ago.
Still have to come up with ideas on what
@Jaz can do about his 8.5 pH tap water. We know that the soil can change the pH of slightly acidic water but how much can it do with water that is alkaline. Did the company that built and sold the soil mix that he is using put something in the soil that will help to change the pH?