A flexible supply line is the short hose that carries water from a wall valve to a washer, dishwasher, icemaker, or faucet. It sits behind an appliance and gets noticed only when it leaks. Treat it as a part with its own date.
Find the line and read it
Walk to each appliance and follow the hose from the wall to the machine. Note the material. Most are braided stainless over an inner tube, and some older ones are plain rubber. Look at the whole length, including the bends and both ends. Check the fittings where the nut meets the valve and where it meets the appliance.
Look for bulges, kinks, cracks in the outer sleeve, white mineral crust at a fitting, and any dampness at a nut. Feel for stiffness. A hose that has gone hard or brittle is telling you something about its age.
Write the install date on it
If nobody recorded when the hose went in, record it now and treat that day as the start of the clock. Write the date on a strip of masking tape at the valve end, or enter it in your owner's file. If the hose has a printed date code, copy that too. The date is a planning input. It tells you when to look again and when to think about a swap. It does not tell you the hose has failed.
Check the shutoff before you need it
Each supply line ends at a shutoff valve. Turn the valve gently closed, then back open, and confirm that it stops flow to that fixture. If it does not close fully, if it is stuck, or if it weeps around the stem, the valve needs a plumber. Do not force a stuck valve, because an old one can break under a hard turn. Note which valve feeds which appliance, so anyone in the house can shut the right one quickly.
What to compare when you replace one
Choose a length that reaches without strain or tight bends. Choose a fitting size and type that matches both the valve and the appliance inlet. Ask the installer or supplier which material they used, and write it in your file. Ask whether the new hose carries a printed date code. Ask how you would shut the water off if you later need to move the appliance.
Compare two options only on those points: length, fitting, material, and what the paper says about age. Do not let price or brand name stand in for those checks.
Who does the work
Replacing a supply line is a small job, and some owners do it themselves. It still means shutting water off, relieving the pressure, and tightening fittings by hand without overdoing it. If the valve is old, if you are not sure which valve feeds which fixture, or if the line runs through a wall or floor you cannot see into, hire a licensed plumber. Record the job in your file either way.
Where it fits on your calendar
Add the supply lines to your walk-through. Check them whenever you pull an appliance out for cleaning or moving, and during the seasonal look at the appliances they serve. For the planning dates on those appliances, see the Clothes Washer page and the Dishwasher page.