when it comes to water, I got my education on 35 years of caring for Koi.
During that time, I did get into Reverse Osmosis systems.
They're not cheap to purchase or maintain. You need to be able to automatically backflush the membraines or they quickly plug. If you can figure out how much water you need per day on the most demanding day, that's how you figure how big a unit to purchase. For example i had
a 4,000 glaaon pond that I gave a 10% water change to so that meant my purchase was a machine that could make 400 gallons a day. If I had a dollar for each time the water department based on my use left me a note to check for a leak in my system I could buy us a nice lunch! What was bad, even tho I bought the best available system at the time, the water wasted and not used was 40%. It's the price you pay for the system. In the beginning of the technology it was more like 40% was usable and 60% went to waste.
While it seems your general Hardness is up there ( with RO I kept mine at 60 GH ) some trees actually do better with a slightly hard water. 7 is neutral on the PH scale and anything below is considered hard. Above soft. ( human blood BTW is 7.2) Things like rhodies, azaleas, Japanese maples liked a ph close to 6.8
Our water here in the pacific NW is basically snow melt from river run off. Not much in the way of minerals but it never seemed to matter as there were suppliments I could use once or twice a year to make sure they got "trace" stuff.
Hope something in my ramble is useful to you.