What It Is
A water supply line is the short flexible tube that connects a plumbing fixture to its shutoff valve - found under sinks, behind toilets, at washing machines, refrigerators, and dishwashers. Many are in the range of 12 to 24 inches long and made from braided stainless steel over a rubber or polymer core, or reinforced polymer, though lengths vary by application. They are among the most common sources of slow household water leaks that go undetected for extended periods.
What It Does
Supply lines bridge the final connection between the rigid supply piping in your walls or floor and the fixture. Because fixtures don't always align perfectly with pipe stubs, flexible supply lines allow small offsets and make installation practical. They are designed to handle constant water pressure but are not built for permanent, decades-long service.
Where It Is Located
Every fixture in the home has supply lines. Common locations:
- Under bathroom and kitchen sinks - one hot, one cold
- Behind toilets - one cold line only
- Behind or under dishwashers - hot water
- At washing machine - hot and cold, typically red and blue braided hoses
- Behind refrigerators with ice makers - cold water only
How It Works
The supply line screws onto the outlet of the shutoff valve on one end, and to the fixture inlet (faucet or toilet fill valve) on the other end. Both connections typically use compression fittings or threaded connections with rubber gaskets. The supply line flexes slightly to accommodate the angle between the valve and the fixture inlet.
Standard residential water pressure (45-75 psi) acts on the supply line continuously whenever the water is on. Braided stainless lines have a better failure profile than plain rubber hoses, but the inner rubber core of any supply line can degrade from age, chlorine exposure, or pressure cycling.
Common Problems or Signs of Failure
- Dripping or wet spot at the connection point under the sink or behind the toilet
- Bulging or blistering of the hose body - imminent failure
- Cracked or corroded fitting ends - especially on older chrome supply lines
- Rubber hose (non-braided) showing cracking, stiffness, or discoloration
- Higher-than-normal water bill with no obvious source - may indicate a slow supply line seep
- Washing machine supply hose that hasn't been replaced in over 5 years
Can a Homeowner Check It?
- Reach under each sink and behind each toilet to feel for moisture on and around the supply lines
- Look at the hose body for bulges, discoloration, or mineral deposits (white staining) near the ends
- Check washing machine supply hoses - these carry higher flow and should be replaced every 5-7 years
- Confirm that shutoff valves at each fixture close fully - test by turning them closed and reopening
- Age: if supply lines are original to a house more than 15 years old, proactive replacement is worthwhile
When to Call a Plumber
Supply line replacement is within the skill set of many homeowners comfortable with basic plumbing. However, call a plumber if the shutoff valve also needs replacement (seized or leaking), if the fixture connection threads are damaged, or if you discover water damage from an undetected supply line failure. A plumber can also replace all supply lines during another service visit as preventive maintenance.
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