Evaporation drops a pool’s water level slowly and evenly, usually a small amount every day, faster in hot, dry or windy weather. A real leak tends to lose water faster than weather alone can explain, keeps dropping even when the pool isn’t running, or shows up alongside wet spots, soggy ground or a rising water bill.
Every pool loses some water just from being outside. Heat, sun and wind pull moisture off the surface constantly, and that’s normal. The question worth answering is whether what’s disappearing lines up with what the weather would predict, or whether it’s more than that. A simple test at home can usually tell the difference before anyone needs to call in help.
What is a normal amount of evaporation for a pool?
Normal evaporation varies a lot by climate, but it’s driven by heat, low humidity, wind, and a warm water temperature relative to the air. A pool in a hot, dry, breezy location will always lose visibly more water than one in a cool, humid, sheltered yard, and that’s expected, not a fault.
Things that speed up evaporation include:
- Direct sun and high air temperatures
- Wind moving air across the water surface
- Low humidity, especially in desert or dry climates
- Running water features, spillovers or fountains, which expose more surface area to air
- Heating the pool, since warmer water evaporates faster than cool water
None of these numbers are fixed, and anyone quoting an exact daily loss figure without knowing local weather is guessing. The reader’s own pool, in their own yard, over a few normal days, is the only reliable baseline. For more on why a pool can lose real water without anything being broken, see why pools lose water with no leak.
How does the bucket test work?
The bucket test compares water lost from a bucket sitting in the pool to water lost from the pool itself. If both drop by roughly the same amount, the pool is likely just evaporating normally. If the pool drops noticeably more than the bucket, something else is pulling water out.
- Fill a bucket with pool water and place it on a step or float it in the pool, weighting it slightly so it sits at roughly the same depth as the water outside it.
- Mark the water level inside the bucket and the water level of the pool itself, using tape or a marker.
- Turn off the pump for the test period if possible, or note that it ran, since a running pump changes splash-out and skimmer flow.
- Wait 24 hours without adding water or swimming.
- Compare the two marks. Similar drops in both point to evaporation. A bigger drop in the pool than the bucket points to a leak.
Running the test over two or three days gives a clearer picture than a single day, especially if weather conditions changed in between.
What water-loss patterns point to a real leak?
A pattern that keeps losing a similar amount of water whether the pump is running or off, that continues through cool or humid weather when evaporation should slow down, or that comes with visible wet ground, is more consistent with a leak than with evaporation alone.
Other signs worth paying attention to:
- The water level stops dropping at a consistent point, often right at the skimmer opening — this can point to a leak specifically at or below skimmer level.
- Grass or soil near the pool shell stays damp or spongy without rain.
- Cracks appear in nearby decking, or the deck seems to be settling unevenly.
- Chemical use or top-ups are increasing steadily over a few weeks, not just during a heat wave.
- The water bill has jumped without an obvious reason.
A pool that only loses water while the pump is off, but holds steady while it’s running, often points toward suction-side plumbing rather than the pool shell itself, since that plumbing is only under pressure when water is moving through it.
Could the leak be in the equipment instead of the pool itself?
Yes. Many “pool leaks” are actually leaking at a pump seal, a valve, a heater connection, or a pipe joint on the equipment pad, not through the liner or shell. These leaks often show as damp concrete, drips, or a puddle near the equipment rather than a dropping pool level alone.
Worth checking, without opening anything up:
- Damp patches or mineral staining around pump housings, unions or valves
- Water pooling under the filter or heater even when it hasn’t rained
- A pump that seems to be running louder, or losing prime more often than usual
Understanding what each piece of equipment is supposed to do makes it easier to describe the problem accurately to a professional. What a pool pump actually does and the difference between a skimmer and a main drain are useful starting points, and the Pumps, Filters & Heaters hub covers more on how this equipment is meant to run day to day.
Any repair involving pump wiring, heater electrical connections, bonding or grounding is licensed electrical work. This isn’t a place for guesswork or a weekend fix — a qualified electrician or pool professional should handle anything beyond visually checking for a drip.
What about a leak in the liner, tile or structure?
A liner, fiberglass shell or concrete structure can develop a leak at seams, fittings, tile grout lines, or cracks, and these often show as a slow, steady loss rather than a sudden drop. Structural leaks are harder to confirm without professional dye testing or pressure testing of the plumbing.
Some visual clues worth noting, without attempting a repair:
- A liner that looks like it’s pulling away from the wall or floor in one spot
- Cracked or missing grout around waterline tile
- A visible crack in fiberglass gelcoat or concrete, even a hairline one
- Air bubbles coming from a fitting like a light niche, return jet or main drain
How a pool is built affects how it tends to leak and how leaks are usually fixed — a vinyl liner, fiberglass shell and concrete pool each have different failure points and repair approaches. Comparing vinyl liner, fiberglass and concrete pools covers those differences in more detail.
Structural repairs, excavation around a shell, or replastering are specialist jobs governed by local building code in most areas. They’re not something to attempt without a licensed contractor, and permit requirements vary by location — always check local code before any structural work is planned.
When is it time to call a professional leak detection service?
It’s worth calling a professional once the bucket test shows loss beyond what evaporation explains, once equipment-pad dampness or wet ground appears, or once a level of confidence is needed that DIY checking can’t provide — for instance, before a costly repair or a home sale.
Professional leak detection typically involves dye testing at suspect fittings, pressure testing sections of plumbing, and sometimes specialized listening or camera equipment to trace a leak underground or in a wall. This is a different skill set from routine pool maintenance, and it isn’t reasonable to expect to trace a slab leak or underground pipe leak with a bucket and a flashlight. Costs for professional leak detection vary widely depending on pool size, how straightforward the leak is to locate, and regional labor rates — it’s fair to ask a few local companies for a walk-through and a written estimate rather than expecting a fixed number in advance. The Buying & Costs hub has more on how to think through pool-related costs generally.
In the meantime, keeping circulation running as designed helps avoid other problems while a leak is investigated — see why a pool needs daily circulation and what turnover rate means for water quality for background on why steady circulation matters even during a leak investigation. For a broader refresher on how water actually moves through a pool system, how a swimming pool circulates water is a good primer, and the Pool Basics hub covers related fundamentals for new and long-time owners alike.
Pools Shop publishes general information, not professional advice. Pool chemicals, electrical work and structural work are genuinely hazardous and are governed by local codes that vary — use a qualified professional for anything you are not certain about, and follow the instructions on the product in front of you rather than a general guide. Nothing here is a substitute for active adult supervision around water: no cover, alarm, fence or device makes a pool safe on its own.