Leaks & Detection
How to Find a Leak in a Pool
Pools lose some water every day to evaporation. The hard part is telling normal loss from a leak. The steps below cost little and can narrow the leak to the shell, the fittings or the plumbing. If the evidence points to the underground lines or you cannot find it, our team offers pool leak detection in McLean and repairs the plumbing side.
This is general information. Follow your pool manufacturer's instructions and safety guidance.
Step 1: Do the bucket test
The bucket test compares evaporation to the pool's actual loss in the same conditions.
- Fill a bucket with pool water to about the same level as the pool.
- Set it on the first or second step so it sits in the pool water at the same temperature.
- Mark the water level inside the bucket and on the pool wall or skimmer.
- Turn off the auto-fill. Run the pump as usual.
- After 24 hours, compare the two drops.
If the pool dropped more than the bucket, you likely have a leak. Repeat with the pump off for another 24 hours.
Step 2: Compare pump on and pump off
| Result | Where to look |
|---|---|
| Loses more with the pump on | Return (pressure) side plumbing or equipment |
| Loses more with the pump off | Suction side plumbing or the shell |
| Same either way | Shell, light niche, liner or fittings |
| Stops dropping at a certain level | The leak is at that level: skimmer, tile line, light or return |
Step 3: Check the equipment pad
Look closely at the pump, filter, heater, valves and unions. Wet ground, drips, white mineral trails or a pump that sucks air are clues. Leaks here are often easy to fix.
Step 4: Look for common leak spots
- Skimmer throats and seams.
- Return jets and their fittings.
- Main drains.
- Light niches and conduit.
- Tile lines and coping.
- Tears in vinyl liners, especially at steps and corners.
- Spa spillovers and water features.
Step 5: Use a dye test
With the pump off and the water still, squeeze a little dye near a suspected spot. If the dye drifts into a crack or fitting, water is escaping there. Go slowly and stay close to the surface you are testing.
How to find a leak in a pool's underground plumbing
If the shell and fittings look fine but the pool still leaks, the problem may be in the buried lines between the pool and the equipment. Finding those needs pressure testing. Each line is plugged and pressurized; a line that cannot hold pressure is leaking. Acoustic listening then helps pinpoint where along the run. These are the same tools used for leak detection inside homes.
Does the auto-fill hide leaks?
Yes. An auto-fill valve keeps the level steady, so a leak may only show up as a higher water bill. Turn off the auto-fill during the bucket test. Also check that the auto-fill valve is not stuck open or leaking itself. The EPA's WaterSense program estimates household leaks waste nearly 1 trillion gallons nationwide each year, and outdoor leaks are part of that.
Who fixes a pool leak?
| Leak location | Who usually fixes it |
|---|---|
| Underground plumbing lines | Plumber |
| Equipment pad, valves, unions | Plumber or pool service |
| Auto-fill line | Plumber |
| Skimmer, return fittings | Pool contractor or plumber |
| Shell cracks, tile, liner | Pool contractor |
Plumbing repairs to pool lines can count as replacing or repairing plumbing equipment, which Fairfax County lists among the jobs that need a residential plumbing permit. If a leak has damaged a basement, deck or neighboring structure, Virginia's Bureau of Insurance advises giving your insurer immediate notice of a possible claim.
How do I prevent pool leaks?
- Winterize lines correctly before closing the pool so water cannot freeze and split them.
- Check the equipment pad monthly in season.
- Watch for soggy ground or settling around the deck.
- Track your water bill each summer.
- Keep the water level within the skimmer's normal range.
Local note: In-ground pools are common on larger lots in Great Falls, Vienna and Oakton. Long runs to a distant equipment pad give leaks more places to hide.
Related reading: See what sets leak detection cost, try the water meter leak test, and learn how to prevent frozen pipes before you close the pool.
When should you call a pool leak professional?
Call when the bucket test confirms a leak you cannot find, when the pool loses more with the pump running, when there is soggy ground near the lines, or when the auto-fill runs constantly.
Pool leak in McLean? Call (571) 760-4451 for pool leak detection from McLean Plumber Works.
Frequently asked questions
How much water loss is normal for a pool?
It depends on sun, wind, humidity and temperature. That is why the bucket test matters: it measures evaporation in your own conditions and compares it to the pool.
Can a pool leak through the plumbing and not the shell?
Yes. Underground suction and return lines, the equipment pad and the auto-fill line are common leak points that have nothing to do with the shell.
How do I do a dye test?
With the pump off and water still, squeeze a little dye near a suspected crack, fitting or seam. If the dye is pulled toward the spot, water is escaping there.
Does a leaking pool raise my water bill?
Yes, especially with an auto-fill that tops up the pool quietly. A higher summer bill can be a sign.
Should I drain the pool to find the leak?
No. Draining can damage some pools and removes the water you need for testing. Professional leak detection works with the pool full.
Sources
Related guides
Pool losing water? Call for pool leak detection.
Call McLean Plumber Works any time, day or night. A plumber picks up and talks you through next steps.