How the two usually show up
Hot-water side
- Warm or hot patch of floor, often along a line from the water heater
- Water heater runs more often or hot water runs out sooner
- Leak indicator stops when the heater's cold inlet is closed
- Can raise gas or electric use as well as water use
- Line moves more with temperature, so wear spots can recur
Cold-water side
- No warm spot; often found by the bill or the meter
- Damp flooring or wet soil may be the first visible sign
- Leak indicator keeps moving with the heater inlet closed
- Toilets and irrigation must be ruled out first
- Can be under the slab or in the line outside the house
Isolating the side at home
- Confirm a leak.With all fixtures and irrigation off, check that the meter's leak indicator is moving.
- Close the heater's cold inlet.Turn the valve on the cold pipe feeding the water heater. Do not adjust the gas valve, thermostat or burner.
- Watch the meter.Give it a few minutes. A stopped indicator points to the hot side; continued movement points to the cold side or a fixture.
- Write it down.Note the result, the time and whether you felt any warm spot. A plumber will ask.
Why the hot side gets more attention
Hot-water supply lines expand and contract every time hot water runs. Under a slab, that repeated movement can rub the pipe against concrete, gravel or another pipe until a thin spot opens. Many of Fullerton's slab homes route the hot line from a water heater in a garage or hall closet under the floor to bathrooms and the kitchen, so a leak along that path is a familiar pattern.
Hot-side leaks also cost twice: you pay for the water and for the energy that heated it. That is one reason not to let a suspected hot-side leak run for weeks.
How the side can affect repair choices
| Situation | What plumbers often discuss |
|---|---|
| First hot-side leak, line in fair shape | Spot repair, or rerouting the hot line above the slab if the location is hard to reach. |
| Repeat hot-side leaks | Rerouting the hot line, since the remaining under-slab section may be similarly worn. |
| Cold-side leak under the slab | Spot repair or reroute, depending on location and pipe condition. |
| Leaks on both sides over time | Whether a repipe of the house makes more sense than repeated repairs. |
Questions for the plumber
- Did your testing confirm the same side my meter test pointed to?
- If it is the hot line, would you reroute the whole hot run or just the leaking section?
- Can the water heater stay in service during the repair?
- Is there a reason to look at the cold line at the same time?
Common questions
Can I just turn off the water heater?
Turning off the heat does not stop the leak; water keeps flowing through the hot line. Closing the cold inlet valve is what stops flow to the hot side.
Does a hot-side leak make the floor hot everywhere?
Usually only in a patch or strip near the leak or along the pipe path, and it may be subtle on carpet.
Is a cold-side leak less urgent?
Not necessarily. It wastes less energy, but water under a slab can still affect flooring and soil, so it is worth locating soon.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.