A refrigerator line filter is one of the few water treatment installs a homeowner can do in an afternoon. It is also one of the easiest to get slightly wrong, and a weeping fitting behind an appliance can go unnoticed for a long time. Work in the order below and check every joint twice.
Before you start
Read the instructions that came with your filter and confirm three things: the fitting type it uses (compression, push-to-connect, or a quick-connect adapter), the arrow that shows water flow direction, and the tubing size. Filters are directional, and installing one backward is a common mistake that keeps water from flowing at all.
Gather a tube cutter, a towel or two, a bucket, and a wrench sized for the compression nut if your fitting needs one. Clear the floor behind the refrigerator so you can see the whole run of tubing.
Shut off and relieve the line
Close the shutoff valve that feeds the refrigerator, usually a small valve under the nearby sink or on the wall behind the unit. Then open the refrigerator's dispenser briefly to release the pressure left in the line. If water keeps coming, the valve is not fully closed or is not the right one, so stop and find the correct valve before you cut anything.
Cut and connect
Cut the tubing square with a tube cutter. Scissors and knives leave angled or crushed ends that will not seal. Push the tube into the filter's inlet until it reaches the stop mark, then into the outlet side as the instructions direct. Tighten compression nuts hand-tight first, then snug them a small amount with the wrench. Overtightening cracks plastic fittings, and that damage often shows up days later.
Open slowly and flush
Open the shutoff valve slowly, not all the way at once, so the line fills without a surge. Run the dispenser and follow the manufacturer's flushing instructions. Air in the line will sputter, and the first water through will often look cloudy from carbon fines. Keep running until the water runs steady and clear.
Check every joint
Dry each connection with a paper towel, both at the filter and at the valve, then look again after ten minutes and once more after an hour. A joint that looks dry at first can still seep under pressure. Check the towel under the refrigerator and the floor below it, and look behind the unit with a flashlight.
When to call a plumber
Hire the job out if the supply valve will not close fully, if the existing tubing is brittle or stiff, if the fitting type on your filter does not match the valve, or if a leak would reach flooring you cannot easily lift. A plumber can also confirm the valve is working, which is worth knowing before you need it.
Once the install is done, write the filter's replacement interval on the housing with a marker and keep the instructions with your appliance paperwork.