I plumbed my RODI to the cold water pipe supplying the washer. Got most of the parts at Can Tire, pressure guage at Princess Auto (two actually). Copper tee, ball valve, copper to PVC JG type tee fitting with a handy 1/4" valved outlet to the pressure guage, then another adapter that takes the larger fitting down to JG 1/4" size for RODI.
I tweaked my PRV to provide 85 psi downstream vs the standard 60. Not sure I'd want to plumb the RODI in upstream of the PRV where it would have to deal with full city water pressure which can be up to 120 psi where I live. Some of the RODI system components may not be able to handle that long term.
