A dropping water level sends people into one of two mistakes. Either they panic over normal evaporation, or they wave off a real leak as "it's just been hot." Both cost you. In a Piedmont summer, a pool genuinely loses a surprising amount of water to evaporation, and it is easy to talk yourself out of a leak that is quietly undermining your deck. The good news is you can settle the question in your own backyard in one afternoon, before you ever pay anyone to look.
Here is how to tell evaporation from a real leak, where leaks actually hide, how the leaks get found, and why chasing one down quickly matters more than the water bill alone would suggest.
Evaporation versus a real leak: the bucket test
First, know what normal looks like. On a hot, dry, breezy day in July, a pool can lose a quarter inch or more to evaporation, and that is not a leak. The wind and low humidity of a stretch of clear days pull water off the surface fast. What separates that from a leak is a simple, free test you run yourself.
Fill a bucket with pool water and set it on the second step so it is partly submerged, which matches the water temperature to the pool. Mark the water level inside the bucket and the pool level outside it, both with a grease pencil or tape. Turn the pump off and leave it for 24 hours. Then compare. If the pool and the bucket dropped by the same amount, that is evaporation — the same air is pulling water off both surfaces equally. If the pool dropped noticeably more than the bucket, you have a leak. Run it a second day with the pump on to see if the loss changes, because that alone starts to tell you where the leak is.
Pressure-side or suction-side? Let the pump tell you
That pump-on versus pump-off comparison is your first real clue. If the pool loses more water while the pump is running, the leak is likely on the pressure side — the return plumbing that is under pressure when the pump pushes water back to the pool. If it loses more while the pump is off, the leak is more likely on the suction side or in the shell itself, where standing water finds its way out. If it leaks the same either way, you are often looking at a structural crack or a fitting at the waterline. None of this is a diagnosis, but it narrows the hunt considerably before anyone opens anything up.
Where pool leaks actually hide
Water gets out through a short list of usual suspects:
- Plumbing lines. The underground return and suction lines are the classic hidden leak. You cannot see them, and in our soil they are under constant stress (more on that below). A wet, spongy spot in the yard over a buried line is a tell.
- Skimmer and return fittings. The joint where the plastic skimmer meets the concrete shell is a common failure point. It flexes, the seal cracks, and water weeps out behind it. Return eyeball fittings and their gaskets leak too.
- The light niche. The conduit and the seal around a pool light are a frequent, sneaky source. Water can leak through the niche and even track back along the conduit.
- Shell cracks. A structural crack in a gunite shell leaks directly into the ground. These are the ones that matter most and the ones you want found fast.
- Vinyl liner tears. On a vinyl pool, a tear or a failed seam at a fitting, a step, or the floor lets water out. Older liners get brittle and tear where they are stressed.
- The equipment pad. Sometimes the water is not leaving the pool at all — it is dripping off a bad pump seal, a cracked filter, a leaking valve, or a backwash line that is not fully closed. Always check the pad, because these are the easiest to fix and the easiest to miss.
The dye test
Once you have a suspect area, the dye test confirms it. With the pump off and the water dead still, put on a mask, get close to a suspected spot — a crack, a fitting, a skimmer throat — and release a little leak-finder dye or even food coloring right next to it. If there is a leak there, the water movement pulls the dye straight into the crack or fitting like a tiny current. It is low-tech, cheap, and genuinely effective for anything you can see and reach. The catch is it only works on visible surfaces and only in perfectly still water, which is why buried plumbing needs a different approach.
Pressure-testing the lines
You cannot dye-test a pipe you cannot see. To check underground plumbing, a pro isolates a line, plugs it at both ends, and pressurizes it with air or water. A line that holds pressure is sound. A line that bleeds pressure down is leaking somewhere along its run, and from there it gets located with listening equipment that hears the escaping water underground. This is the part most owners cannot do themselves, and it is the reason plumbing leaks are the ones worth calling for.
Why red clay makes plumbing leaks common here
The Triad's heavy red clay is not a neutral backdrop. It swells when it soaks up water and shrinks when it dries out, and it does that cycle constantly through our wet springs and dry late summers. Everything buried in it — the rigid PVC return and suction lines especially — gets pushed and pulled by that movement season after season. Over years, that stress cracks fittings and separates glued joints, which is exactly why underground plumbing leaks are so common in this part of North Carolina. It is also why a leak that starts small tends to get worse: the same ground movement that opened the joint keeps working it.
Why chasing a leak fast actually matters
The water bill is the least of it. A leak that escapes into the ground washes soil out from under your deck and pool surround, and that undermining is what causes decks to crack and settle. Left long enough, a plumbing leak can saturate the soil around the shell and contribute to the kind of movement that stresses the structure itself. On top of that, every gallon that leaks out takes your heat and chemistry with it — you are paying to warm and balance water that runs straight into the dirt, and constantly adding fresh fill water throws your chemistry off, which then chews on your surface. A small, cheap leak found in June is a very different thing from the deck repair it becomes by spring, and it is one of the clearest signs a pool needs attention.
When to call a pro with leak-detection gear
Do the free work first. Run the bucket test, check the equipment pad, and dye-test anything visible — skimmers, returns, the light niche, any crack you can reach. You will solve a fair number of leaks right there. Call a professional when the leak is in the buried plumbing, when the bucket test says you are losing water but you cannot find where, or when a dye test points at a shell crack. Leak-detection specialists have pressure-testing rigs and acoustic listening equipment that find what you cannot see, and a structural crack in particular should be evaluated before you decide between a repair and a resurface. If your bucket test confirms you are losing water, do not wait for the deck to tell you next. Call (336) 471-0103 or request an evaluation and we will find it before it costs you the surround.