Supply Line — What It Is, Where Used, and Replacement Guide

A supply line is the water line that carries pressurized hot or cold water from the plumbing system to a fixture or appliance.

Supply Line diagram — labeled parts, dimensions, and installation context

What It Is

Supply lines connect shutoff valves or branch piping to faucets, toilets, dishwashers, ice makers, and other fixtures. They may be flexible braided connectors, plastic tubing, copper, or other approved materials depending on the fixture and local practice.

Because they stay under pressure all the time, a failed supply line can leak continuously and cause fast water damage.

Types

Common types include braided stainless steel faucet connectors, toilet supply lines, PEX tubing, copper stub-outs with connectors, and appliance-specific water lines. Length, end fittings, and pressure rating have to match the fixture and valve.

Where It Is Used

Supply lines are used under sinks, behind toilets, at dishwashers, refrigerators, water heaters, and many plumbing fixtures. They are the visible link between the water distribution piping and the fixture being served.

How to Identify One

Look under a sink or behind a toilet for a small tube or braided line running from the shutoff valve to the fixture. Hot and cold supply lines are often paired together at sinks and faucets.

Replacement

Replacement is needed when a line kinks, corrodes, drips at the fittings, bulges, or exceeds its expected service life. Braided lines are inexpensive enough that proactive replacement is common during fixture updates.

Supply Line — FAQ

How long do braided supply lines last?

They can last many years, but they do not last forever. Age, water quality, overtightening, and movement can all shorten their service life.

Why is my toilet supply line leaking?

The fitting may be loose, the washer may have failed, or the line itself may be damaged. Corrosion at the shutoff valve can also make it seem like the line is leaking.

Can I reuse an old supply line when replacing a faucet?

It is usually better not to. New lines are cheap compared with the cost of a leak, and old washers or fittings may not reseal well.

Do supply lines need thread seal tape?

Some connections seal with a gasket or cone washer and should not rely on tape. It is better to follow the fitting type and manufacturer's instructions than apply tape automatically.