Are you filtering after the pressure reducer or did you plumb it in for the cold water sink only?
I can see an argument for putting one in either one place or the other. Filter only drinking water OR filter everything to protect the whole plumbing system.
Brian, Michelle and 2 boys
2010 Toyota Tundra Crew Max 5.7L
2015 Jayco White Hawk 33BHBS Summit Edition, Glacier Package