What PoolBoss Says
Confirm the loss rate first, then check the equipment pad and backwash line for visible water. Compare loss with the pump running against the pump off to separate plumbing from shell. Dye-test the skimmer throat, light niche, and return fittings. Call a specialist for pressure testing when the shell tests clean.
A pool that is genuinely losing water is one of the few problems on a route that can quietly eat a whole morning. The tests themselves are cheap. They only work in the right order, and the wrong order is how a tech spends two hours at one stop and still has nothing useful to tell the customer.
What follows is the sequence a route company can actually run: what the pump-on versus pump-off comparison rules out before you touch anything, how to dye-test a suspect point without fooling yourself, which locations are worth your time and which belong to a specialist, and where the honest line sits between chasing a leak and handing it off.
At a glance
Key takeaways
- Start from a measured loss rate, not a suspicion. A quarter inch a day is about 60 gallons on a 400 square foot pool and is worth chasing; an eighth of an inch in peak summer usually is not.
- Walk the equipment pad with the pump running before anything else. A weeping seal or a damp union is the most common finding and often a same-visit fix.
- Check the backwash line with the valve on filter. A trickle there is a bad valve gasket sending water out of the pool, not a structural leak.
- Compare 24 hours pump-on against 24 hours pump-off. Faster with the pump running points at pressure-side plumbing; the same either way points at the shell.
- Dye-test only on still water with the pump off for 15 to 30 minutes, and test the skimmer throat first because it is the most common findable leak.
- Treat two hours as the ceiling on chasing one leak, then refer it out with your loss rate and test results attached so the specialist does not start over.
How do I find a pool leak?
Work the cheapest test first and stop the moment the answer arrives. Leak work goes wrong when a tech opens with the hardest test instead of the two free observations that tell you which half of the system to suspect. Start from a real number: confirming the pool is actually losing water and knowing how fast is what makes every later test readable. One inch off a 400 square foot pool is roughly 250 gallons, so an inch a week is a real loss and worth an hour of your time.
The sequence below is ordered by what it costs you. The first four steps are free and take about twenty minutes spread across a normal visit. Most findable leaks on a service route are found in those twenty minutes, and the ones that are not have already told you enough to hand over.
- Get a loss rate. Mark the waterline with a grease pencil and note the date, and rule out water you removed yourself first, because vacuuming to waste or a backwash drops the level for reasons that have nothing to do with a leak. An eighth of an inch a day in peak summer is usually evaporation; a quarter inch a day, about 60 gallons on a 400 square foot pool, is a leak worth chasing.
- Walk the pad with the pump running. Wet ground, a dripping pump seal, a weeping filter clamp, or a damp union is a visible leak you can often fix on the spot, and it is the single most common finding.
- Check the waste line. With the valve on filter, any trickle out the backwash port is water leaving the pool through a bad valve gasket, not a structural leak at all. That is a filter valve repair rather than a leak hunt, and it is easy to spend a morning missing it.
- Compare pump on with pump off. Twenty-four hours on each setting separates pressurized plumbing from the shell before you spend a dollar. This is the highest-value free test on the list.
- Dye-test the suspect points. On still water, test the skimmer throat, the light niche, and the return fittings in that order. These three account for most of the findable shell-side leaks on residential pools.
- Stop and refer. When the pad is dry, the waste line is clean, and the three dye points hold, the leak is in buried plumbing or under the plaster, and finding it needs equipment you should not own.
Pump on versus pump off tells you plumbing or shell before you test anything
Run the pump for 24 hours and mark the drop, then leave it off for 24 hours and mark it again. The difference between those two numbers is the most useful thing you will learn all week, because the pressure side of the system is only under pressure when the pump is running. A leak downstream of the pump gets pushed harder when the motor is on and nearly stops when it is off.
Read it three ways. If the pool drops noticeably faster with the pump running, the leak is on the pressure side: the returns, the filter, the heater, or the valves after the pump. If it drops faster with the pump off, suspect the suction side or the shell, because a static pool is still losing water through whatever hole exists while the suction lines are no longer pulling. If both numbers are about the same, the leak is almost certainly structural and is not related to the plumbing at all.
This costs nothing but two visits' worth of patience, and it cuts the search area roughly in half before you get wet. It also protects you from the expensive mistake of dye-testing the shell for an hour on a pool whose problem is a cracked return fitting the pressure test would have found in ten minutes.
Dye testing works, but only on a still pool at a suspect point
A dye test is a visual check for water moving into a hole, so anything that moves the water defeats it. Shut the pump off and give the pool 15 to 30 minutes to settle, pull the cleaner, and pick a calm morning. Wind chop across the surface will scatter dye at the skimmer throat and hand you a false negative every time.
Get the dye within an inch of the point you are testing and release it slowly, then watch. A leak draws a thin thread of dye into the crack in a second or two. If it just clouds and drifts, there is no draw there. Test the skimmer throat first, because the joint where the plastic skimmer meets the concrete shell is the single most common findable leak on a residential pool. Then the light niche, where the conduit behind the fixture is a known path, then each return fitting.
The one thing a dye test cannot do is prove a pool does not leak. It only ever tells you about the spot you tested. Three clean dye points mean the leak is somewhere you have not looked, which is a useful result and is exactly the finding that justifies a referral.
Where to test and who should do it
The division of labour is not about skill, it is about equipment. Everything a route tech can find is findable by eye, by hand, or with a two dollar bottle of dye, and it fits inside the equipment walk-around you already do each visit. Everything below that line needs a pressure rig or acoustic gear that costs more than the leak work on a route will ever pay back.
| Where the leak is | How it gets found | Who should do it |
|---|---|---|
| Equipment pad | Look and feel for wet ground with the pump running | Route tech, often fixable same visit |
| Backwash or waste line | Check for a trickle out the line with the valve on filter | Route tech |
| Skimmer throat | Dye at the plastic-to-concrete joint, pump off | Route tech |
| Light niche | Dye at the conduit behind the fixture, pump off | Route tech |
| Return fittings | Dye at each fitting, pump off | Route tech |
| Main drain | Dye at the drain, which means a swim to the deep end | Route tech if comfortable, otherwise refer |
| Buried pressure plumbing | Isolate and pressure-test each line to a gauge | Leak specialist |
| Buried suction plumbing | Pressure test, then acoustic location to pinpoint | Leak specialist |
| Crack under the plaster | Pressure or dye survey across the shell, sometimes a dive | Leak specialist |
The sub-out decision is economics, not pride
Two hours is the honest ceiling on what a route company can spend hunting one leak. Past that you are working for free on a stop that is priced for a 25 minute visit, and the eleven stops behind it are running late. The tests above fit inside that ceiling comfortably, which is the whole reason they are ordered by cost.
Take an operator running 160 pools across Cape Coral and Fort Myers. One Cape Coral pool is down about an inch and a half a week, roughly 375 gallons. With the pump off the loss nearly stops, which points at the pressure side, so the tech dye-tests the return fittings and finds nothing. Two hours in, that is the end of profitable work. The stop goes to a leak specialist with the loss rate, the pump-on versus pump-off result, and the dye results attached, and because the water-level and equipment notes on that pool's record travel with the referral, the specialist starts at the pressure test instead of repeating the first two hours.
That handoff is where the money actually is. A specialist detection visit typically runs a few hundred dollars, and the repair is quoted separately once the leak is located, so quoting the repair before the location is known is guesswork you will regret. Stay the coordinator: you make the referral, the customer stays yours, and the visible record of what you already ruled out is what stops the specialist from billing your customer twice for the same twenty minutes.
FAQ
Frequently asked questions
Should my company buy leak detection equipment?
Almost certainly not. Acoustic listening gear and a proper pressure rig run into the thousands of dollars and take real practice to read, and a route company simply does not find enough leaks to earn that back. The honest math is that leaks are a small fraction of stops, and the ones you can find pay for a bottle of dye and nothing more. Buy the cheap end of the kit instead: a few bottles of leak-finding dye, a grease pencil for marking the waterline, and a decent pair of goggles. That covers every test worth your time. The equipment above that line belongs to the specialist you refer to, and being the person who refers well is worth more to your business than owning a tool you use four times a year.
How do I bill for the time I spend looking for a leak?
Bill it as a diagnostic visit at your normal service call rate, quoted before you start, not folded into the regular cleaning price. A recurring service price covers a 25 minute maintenance stop; it does not cover an hour on your knees at the equipment pad. Tell the customer up front what the diagnostic costs and cap it at the two hours of testing that is actually worth doing. Most customers accept this readily once they understand the alternative is paying a specialist for the same first two hours. If you find and fix something simple at the pad, roll the diagnostic into the repair invoice and everyone feels well served. If you find nothing and refer it out, you still bill the diagnostic, because ruling out the cheap causes is real work that saves the specialist time.
Can I dye test a pool with the pump running?
No, and this is the mistake that produces most false negatives. With the pump running, water is being pushed out of the return fittings, so dye released at a pressure-side leak gets blown away from the crack rather than drawn into it. You will watch the dye disperse and conclude the fitting is fine when it is the actual leak. Shut the pump down and give the water 15 to 30 minutes to go genuinely still before you test anything. The one narrow exception is confirming a suspected suction-side draw, where running the pump briefly can exaggerate the pull at a skimmer throat, but it is a confirmation of something you already suspect rather than a way to search. When in doubt, test still.
What do I do when the customer refuses to call a leak specialist?
Put the cost of not fixing it in writing and keep servicing the pool. A pool losing an inch and a half a week is roughly 375 gallons, plus the chemicals to rebalance the fresh water and the gas to reheat it, and on many pools the annual cost of the leak exceeds the detection visit within a season. Show that arithmetic once, in a note on the account, and let it sit. Do not keep re-testing the pool for free on each visit, because that turns their deferred decision into your recurring unpaid work. Note the water level on each visit so the record shows the trend, and revisit the conversation when the loss gets worse or when equipment starts running dry. Some customers only move once the pump loses prime.
Does a leaking pool ever fix itself when the water drops?
It does not fix itself, but it often appears to, and where it stops is a genuinely useful clue. Water only escapes through a hole that is below the waterline, so when the level falls past the leak the loss stops and the pool holds steady at that height. A pool that stabilizes just below the skimmer throat is telling you the leak is at the skimmer. One that settles a few inches under the returns points at a return fitting or the line behind it. One that keeps dropping toward the main drain suggests something deep in the shell or the drain plumbing. Record the height where it stabilizes before you refill, because that single measurement narrows the search more than an hour of dye testing.
How do I document a leak so the specialist does not start over?
Send four things: the measured loss rate with the dates you marked the waterline, the pump-on versus pump-off comparison, the list of points you dye-tested and the result at each, and photos of the equipment pad. That package is worth an hour of the specialist's time, and a good one will tell you so. Without it they repeat every test you already ran and bill your customer for it, which makes your referral look expensive rather than helpful. Keep the notes on the pool's own record rather than in a text thread, so the history is still there when the same pool leaks again in three years. The height at which the water stabilized is the single most valuable line in that note.
