Installing a Water Filter Under Your Sink

Bottled water adds up fast, both in cost and in the amount of plastic piling up in the recycling bin. An under-sink water filter solves that problem at the tap, and installing a basic system is one of the more approachable plumbing upgrades a homeowner can take on themselves.

What you'll need

• Under-sink filter kit (check that it includes a saddle valve or T-adapter, tubing, and a separate faucet)
• Adjustable wrench
• Drill with a bit sized for your countertop or sink deck (usually 3/8 inch or 1/2 inch, check your kit)
• Plumber's tape
• Bucket and towels

Installation steps

1. Choose where the new faucet will go. Most kits include a small dedicated faucet for filtered water, separate from your main kitchen faucet. Decide where it'll sit, usually next to the existing faucet, and confirm there's a clear path to drill through the sink deck or countertop without hitting a support brace or the sink's rim underneath.
2. Shut off the cold water supply. Locate the cold water shutoff valve under the sink and turn it off. Open the main faucet to release any remaining pressure in the line before you start disconnecting anything.
3. Drill the hole for the new faucet. Using the appropriately sized bit, drill through the countertop or sink deck at your chosen spot. Go slowly, especially through stone or thicker countertop material, and clear away debris as you go. Some kits include a template to guide bit size and placement, worth checking before you drill.
4. Install the new faucet. Feed the new faucet's tailpiece down through the hole from above, then secure it from underneath with the mounting hardware included in the kit. Snug the nut by hand and then with a wrench, careful not to overtighten against the countertop material.
5. Tap into the cold water line. This is the step that makes people the most nervous, but it's more straightforward than it sounds. Most kits use a saddle valve or T-adapter that connects between the existing cold shutoff valve and the supply line running to your main faucet, giving you a second outlet without cutting any pipe. Follow your kit's specific instructions closely here, since the exact fitting varies by brand.
6. Mount the filter housing and connect the tubing. Choose a spot inside the cabinet with enough clearance to change the filter cartridge later, then mount the housing bracket to the cabinet wall. Connect the supplied tubing from the cold water tap, through the filter housing, and up to the new faucet, following the flow direction indicated on the housing. Push-fit connections should seat firmly with a slight tug to confirm they're locked in.
7. Flush and test. Turn the cold water supply back on slowly and check every connection for drips before walking away. Run the new filtered faucet for several minutes to flush out any loose carbon dust from the new cartridge, which is normal for the first use and will clear up quickly.

When to hesitate before doing this yourself

If your cold water line uses an older shutoff valve that feels stiff or won't fully close, or if you're not comfortable working with a saddle valve tap into a pressurized line, this is a reasonable point to bring in help rather than risk a slow leak building inside a closed cabinet where you won't notice it right away.

Most under-sink filter installations go smoothly with a clear kit and a little patience, but if you'd rather skip the trial and error, or your setup doesn't match a standard configuration, ProFlow Plumbing can get it installed correctly the first time and make sure every connection is sealed before you start relying on it daily.