My place is in Tigard, about 20-40tds max out of the tap.
I have never use RO unit because when you have low TDS out of the tap just not required
But I do have 2 unit catalytic carbon 1cuft each canister, 1KDF55 20" canister, 1KDF85 20" canister, and 2 unit of Mix Di Resin 1cuft each, this is for 0 reject water.
This set up last 6 months to show 1TDS and still 0 chlorine and 0 chloramine, but I change it anyway every 6 months
The better prefiltration set (sediment & catalytic carbon) before the RO unit will make the RO membrane last longer and lower volume of reject wat