
I use this filter for my kitchen sink's cold water supply. It doesn't use the same fittings so you'll have to go to a plumbing store but they know what you need. It's not true reverse osmosis filtration, but for flavor polishing and capturing relatively large diameter contaminants, it's a cheap solution.

NANPU 1/2" NPT Air Drying System - 5 Micron Particulate Filter, 0.01 Micron Coalescing Filter, Air Pressure Regulator Combo - Semi-Auto Drain, Poly Bowl W/Metal Gauge
23 Review

NANPU 1 FRL Air Filter Regulator Lubricator Combo With 0-150 Psi Gauge, 5 Micron Brass Element, Poly Bowl & Semi-Auto Drain - Metal Bracket Included
20 Review

NANPU 3/8" NPT Compressed Air Filter Regulator Combo Piggyback, 5 Micron Brass Element, Poly Bowl, Semi-Auto Drain, Metal Bracket, 0-150 Psi Gauge
26 Review

Filter under the sink Aquaphor Favorit ECO silver
20 Review