Installing an under sink water filter is one of the most practical home improvement projects you can do. It takes about one hour, requires no plumbing experience, and gives you filtered water directly at your kitchen tap. Most modern systems come with everything you need in the box. This guide walks you through the complete process.
What You Will Need
- Under sink water filter kit (includes filter housing, cartridge, tubing, and fittings)
- Adjustable wrench or channel-lock pliers
- Drill and drill bit (if installing a dedicated filter faucet)
- Teflon thread seal tape
- Bucket and towels
- Permanent marker
Types of Under Sink Filters
Before starting, know which type you have:
- Standard single or multi-stage filter: Connects inline to your existing cold water supply line. Water still comes out of your regular faucet. Easiest to install.
- Dedicated faucet system: Includes a separate faucet for filtered water that mounts on your sink or countertop. Requires drilling a new hole if one does not exist.
- Reverse osmosis system: Similar to the dedicated faucet type but with more filter stages and a storage tank. The installation process is the same but takes slightly longer.
Step 1: Turn Off the Cold Water Supply
Locate the shutoff valve under your sink — it is the valve on the cold water line (usually on the right). Turn it clockwise until it stops. Turn on the kitchen faucet to release any remaining pressure and drain the line. Place a bucket under the work area to catch drips.
Step 2: Install the Dedicated Faucet (If Applicable)
If your system includes a separate filter faucet and your sink does not already have an extra hole, you will need to drill one. Most sinks have a pre-drilled blank plug on the deck. Remove it using a screwdriver or wrench. Insert the faucet stem through the hole, add the rubber gasket and mounting nut underneath, and tighten with a wrench. Do not overtighten — fingertight plus a quarter turn is enough.
Step 3: Mount the Filter Housing
Most under sink filter housings include a bracket that screws to the cabinet wall or base. Choose a location that is accessible for future cartridge changes, close to the cold water supply line, and away from the drain line. Mark the screw holes with a marker, drill pilot holes if needed, and attach the bracket. Hang the filter housing on the bracket.
Step 4: Connect the Cold Water Supply Line
This is where you tap into the existing cold water supply.
- Using the included tee fitting: Disconnect the cold water supply line from the shutoff valve. Install the included tee fitting on the shutoff valve. Reconnect the original supply line to one port of the tee and run the new supply tube to the filter inlet. Wrap all threaded connections with Teflon tape before assembling.
- Using a saddle valve (some kits): Clamp the saddle valve onto the cold water pipe and tighten the screw to pierce the pipe. This is the fastest method but considered less reliable long-term — a tee fitting is preferred.
Step 5: Connect the Outlet Tubing
Run the tubing from the filter outlet to either your existing faucet (for inline systems) or the dedicated filter faucet. Most modern systems use push-to-connect fittings — simply push the tubing firmly into the fitting until it clicks. Give it a gentle tug to confirm it is locked.
If your system includes a storage tank (RO systems), connect the tank line to the designated port on the filter unit as shown in your instruction diagram.
Step 6: Install the Filter Cartridge
Insert the filter cartridge into the housing according to the manufacturer’s instructions. Some systems have a specific orientation — check for arrows indicating the flow direction. Hand-tighten the housing cap. Do not use tools to close it, as overtightening makes future changes difficult.
Step 7: Turn On the Water and Check for Leaks
Slowly turn the cold water shutoff valve back on. Check every connection point for drips — the tee fitting, both ends of any new tubing, and the filter housing cap. Tighten any connections that show moisture. Do not use the wrench on plastic fittings — just fingertight adjustments are enough.
Step 8: Flush the System
New filter cartridges contain carbon fines (harmless black particles) that need to be flushed out. Run cold water through the filter faucet for three to five minutes, or until the water runs clear. Discard this initial water. Some manufacturers recommend flushing a full gallon before drinking.
Maintenance Schedule
Mark the installation date on the filter housing with a permanent marker. Set a calendar reminder to replace the cartridge based on the manufacturer’s recommendation — typically every six months or 500 gallons for standard carbon filters. RO membrane replacement is usually needed every two years.
Bottom Line
An under sink water filter installs in about an hour and gives you clean, filtered water directly from your kitchen tap. Follow the steps above, take your time with the connections, and do a thorough leak check before considering the job done. Your only ongoing task is replacing the cartridge on schedule.
Disclaimer: If you are not comfortable working with plumbing, hire a licensed plumber to install your filter system.