How to Install a Reverse Osmosis Drinking Water System

Reverse osmosis systems sit under your kitchen sink and filter water down to the molecular level, removing dissolved minerals, chlorine, and other contaminants. What comes out is cleaner, better-tasting drinking water—and you get it on demand without buying bottled water. The system works by forcing water through a semipermeable membrane under pressure, which sounds complicated but the installation itself is straightforward plumbing work. You're essentially tapping into your cold water line, running it through filters and a membrane, and sending the clean water to a dedicated faucet while sending the wastewater down the drain. Most homeowners handle this in an afternoon without calling a plumber, and you'll feel that satisfaction every time you pour a glass of clean water from your new faucet.

1. Clear the Workspace. Close the shut-off valve under your sink—turn it clockwise until it stops. Open the faucet above to release any remaining water pressure, then place a bucket underneath the cold water supply line where you'll be working. Clear out everything under the sink so you have room to maneuver and install the system's housing unit.
2. Tap the Supply Line. The saddle valve clips directly onto your existing copper or plastic cold water line without cutting. Position it on a horizontal section of pipe near the shut-off valve. Tighten the clamp bolts evenly on both sides—snug but not gorilla-tight, or you'll crack the valve body. Attach the inlet tube from the RO system to the saddle valve outlet using the compression fitting provided.
3. Secure the Housing. Set the RO system's filter housing bracket against the wall or cabinet side under the sink, leaving enough clearance for the filter cartridges to slide in from below. Mark the mounting holes with a pencil, then drill pilot holes and secure the bracket with the provided screws. Make sure it's level and stable—this unit will get bumped by feet and vacuum hoses.
4. Install the Cartridges. Run the inlet tube from the saddle valve down to the top inlet port of the filter housing. The system usually comes with three cartridges: sediment, carbon, and reverse osmosis membrane. Slide each one into its respective chamber from below, then hand-tighten the plastic caps at the bottom of each chamber until they're snug. Don't overtighten—these plastic threads strip easily.
5. Route the Wastewater. Attach the drain tube from the RO housing to a drain saddle clamp that clips onto your P-trap or main drain line. The saddle clamp pierces the drain line without cutting—position it on the section of pipe between the sink and the wall. The RO system's wastewater will flow backward through this connection into your main drain, sending reject water down the waste line.
6. Install the Spout. Drill a hole in your sink or countertop for the RO faucet if one doesn't already exist—typically ¾ inch diameter. Feed the faucet body through the hole from underneath, then tighten the nut that secures it from below. Attach the output tube from the RO housing to the inlet port on the faucet base using the compression fitting. This is the line that delivers your clean drinking water.
7. Prime and Pressure-Test. Open the shut-off valve slowly and let water run through the system for 15 minutes to rinse out carbon fines from the filters—the water may look cloudy or taste odd. Check every connection point for drips by running water and waiting five minutes. Tighten any leaking connection with a wrench, but don't force it. After flushing, drain the first gallon of RO water into the sink before using the system for drinking.
8. Schedule Filter Changes. Mark the installation date on the filter housing or a sticky note taped underneath the sink. RO filters typically last 6–12 months depending on your water quality and usage. Set a phone reminder for 6 months out to replace the sediment and carbon filters. The RO membrane lasts longer—usually 18–24 months—but check your system's documentation to be sure.