We can never be 100% sure of the direct causation when observing discoloration, interruptions in growth, necrosis, etc. When a change is made and improvement is noted we can make some educated assumptions.
Before switching to the carbon filtered water I noted multiple issues that pointed to lacks of specific nutrients, even though I was supplementing them. That's when I started to think the issue was uptake of nutrients, not just the presence or absence of them.
Within a couple weeks of switching to the carbon filtered water I saw improvement and since then I've never had large scale issues again.
Indoors I've grown multiple cultivars of chili pepper, scallions, shallots, small tomatoes, radish, and strawberries.
Ornamental flowers here and there over the years..
Also cannabis.
All of the above have shown some level of improvement with the water change, none more than others I think. Always found the strawberries to be extra finicky though.