In Florida, your pool loses water to evaporation year-round — only the cause changes with the season. Hot summers heat the water and drive evaporation up. Cold dry, windy winter air does the same thing from the other direction. On either kind of day, losing a quarter-inch can be completely normal, even though it looks like a leak. Knowing what drives evaporation helps you understand what's actually happening.
What drives evaporation.
Evaporation is a function of the difference between water temperature and air temperature, the humidity of the air above the water, and how much that air is being replaced by drier air (wind). More heat on the water, drier air above it, and more wind moving that air away — all increase evaporation. Here's how the key factors weigh:
Water temperature
Warmer water evaporates faster, which is why a heated pool in winter can match or beat an unheated pool in summer.
Humidity
Dry air absorbs more water. Florida's humidity usually slows evaporation — but not during cold fronts.
Wind
Wind replaces humid air at the pool surface with dry air, accelerating evaporation significantly.
Sun exposure
Direct sun heats the water surface and increases evaporation. Shaded pools evaporate noticeably less.
Screen enclosure
A screen cuts wind exposure and traps humidity. Screened pools typically evaporate 30-50% less than open pools.
Water features
Fountains, waterfall, deck jets, and spillovers dramatically increase evaporation by creating surface area.
Pool cover
A solid pool cover can reduce evaporation by 90%+. Few Florida residential pools use them, but they work.
Swimming
Splashing and splash-out are real water loss but they're not a leak. Common after parties or heavy use.
Typical Florida evaporation rates.
For most Florida pools under normal conditions, daily evaporation falls between 1/16 and 1/4 inch. The upper end of that range — closer to 1/4 inch — tends to occur on windy days or when pool water is significantly warmer than the air. Screened pools typically land at the lower end. The only conditions that push meaningfully above 1/4 inch are a heated pool running through a cold front with wind on an unscreened surface — an uncommon combination.
How much water are you actually losing?
Before diagnosing anything, it helps to translate inches into gallons — the volume is what separates normal from not-normal. A lot of our leak detection calls come in right around the 1-inch-per-day mark; that seems to be the threshold where pool owners start seeing the loss as unmanageable.
How much water is 1 inch on your pool?
For a rectangular pool, gallons per inch equals length × width × 0.62. A few common sizes:
14 × 28 pool → 244 gallons per inch
15 × 30 pool → 279 gallons per inch
16 × 32 pool → 318 gallons per inch
18 × 36 pool → 402 gallons per inch
20 × 40 pool → 496 gallons per inch
25 × 50 pool → 775 gallons per inch
Irregular shapes average somewhere between rectangle and freeform — count on roughly 75-80% of the rectangular number.
Don't want to do the math? Our Water Loss Calculator turns your pool's dimensions and daily drop into exact gallons lost in seconds.
So when someone tells us their 18×36 pool is losing "an inch a day," they're actually losing about 400 gallons a day. Even at peak Florida summer evaporation, a pool rarely loses more than 1/4 inch per day — so a full inch is almost always a real leak. If it is, you're looking at 12,000+ gallons a month going somewhere it should not.
The bucket test:
the only truly reliable answer.
Every other method of evaluating pool water loss involves guessing at evaporation rates. The bucket test bypasses the guessing. Because the bucket and the pool share the same weather, temperature, humidity, and wind conditions over the same 24 hours, the evaporation from both should be identical. Any difference is leak loss.
It's been around forever and most pool owners have heard of it — but almost no one runs it correctly. Here's how to do it right:
- Get a 2–5 gallon bucket and fill it with pool water to within an inch of the rim.
- Place it on the pool steps so the bucket is partly submerged. This equalizes water temperature — critical for accuracy.
- Mark both water levels. Mark the pool's level on the tile or inside the skimmer, and the bucket's level on the inside of the bucket.
- Wait 24 hours with the pump running on its normal schedule. Don't swim, add water, or touch the bucket.
- Compare the drops. If the pool dropped more than the bucket, the difference is how much you've lost from the leak.
How to read the result
Both dropped the same amount: Evaporation only. No leak.
Pool dropped more than bucket: You have a leak. The difference is the leak rate.
Bucket dropped more than pool: Run the test again — something interfered (wind, bucket tipped, inaccurate mark).
Two situations where the bucket test alone isn't enough:
Variable water features
If your pool has a waterfall, spillover spa, or deck jets that run on a timer, the test needs to reflect normal conditions. Run the test with features set to their regular schedule. Testing with features off will show lower evaporation.
Intermittent leaks
Some leaks only leak under specific conditions — pump running, heater active, specific water level, spa spilling over. A 24-hour test that doesn't include the triggering condition can miss the leak entirely. If bucket tests are ambiguous across multiple trials, that's a clue toward an intermittent pattern.
When evaporation looks like a leak.
There are specific scenarios where normal evaporation gets mistaken for a leak — some of our most common second-opinion calls start here:
Scenario 1: Heater added to existing pool
Adding a heater can double your pool's evaporation rate. Owners call convinced the heater installation caused a leak. Usually it just exposed normal heated-pool evaporation numbers.
Scenario 2: Screen enclosure damaged or removed
Hurricane damage, renovation, or removal of a screen enclosure can roughly double evaporation. Pools that evaporated 1/8 inch before are now doing 1/4 inch or more, and owners understandably assume the damage caused a leak.
Scenario 3: New water feature installed
Adding a waterfall, spillover, or bubbler adds significant surface evaporation. A new "leak" that appeared right after a remodel is often just the features doing what features do.
Scenario 4: Vacation home that was recently used
Vacation rentals often see heavy use when they're occupied — large families mean a lot of splash-out. After the guests leave and the home is inspected, that drop in water level can easily get mistaken for a leak.
Scenario 5: Seasonal change
The shift between seasons often increases evaporation by widening the gap between water and air temperature — warm pool water against cooler, drier air pulls moisture off the surface faster. Seasonal changes also tend to bring stronger winds, which accelerate evaporation even further. A pool that held steady all summer can suddenly start dropping faster, and that change gets mistaken for a leak.
When the bucket test says evaporation,
but it doesn't feel right.
Occasionally a client runs a bucket test that shows even evaporation, but they're still convinced something is wrong. In most cases, the bucket test is right — but here are the legitimate exceptions:
Bucket placement inconsistency. If the bucket is in shade and the pool is in full sun (or vice versa), results are misleading. The bucket should experience the same sun exposure as the average of the pool surface.
Marking error. 1/16-inch differences are within the margin of human marking error. True leaks of that size are rare but exist.
If the bucket test confirms a leak: what's next?
Once the bucket test confirms you have a leak, it's time to give us a call. The sooner a leak is located and repaired, the less damage it does — water escaping into the ground around a pool erodes soil, causes settlement, and turns a straightforward repair into a much larger one over time.
Loss only when the pump runs
This pattern can point to a few different sources. An attached spa is a common one — when the pump runs, water circulates and the spa level rises, potentially pushing water above a crack or gap that's otherwise dry. It can also mean an equipment-side leak: a failed D.E. waste valve, a leaky union on the filter, or similar pad equipment that only has water flowing through it when the pump is on. Solar panels are another possibility — they're only primed and pressurized when the pump runs, so a leak in the panels or their plumbing won't show up at all when the system is off.
Loss only when the pump is OFF
One common cause is a suction-side pipe break. During pump operation, the broken pipe draws in air rather than leaking water outward — so the loss isn't visible while the system runs. Once the pump shuts off, water bleeds out through the same break. Another possibility is a siphoning issue with an attached spa: when the pump turns off, the spa can backflow into the pool and raise the water level above an overflow pipe or fitting, causing water to drain out in a way that only happens at rest.
Loss about the same whether pump runs or not
This points to a structural or waterproofing-related leak — one that's losing water regardless of what the equipment is doing. Common sources include separations in the plaster or waterproofing around penetrations, shell cracks, bond beam cracks behind the tile line, leaking light fixtures, and cracked skimmer bodies.
Loss stops at a specific water level
Knowing where the water level stops dropping is one of the most helpful clues a homeowner can give us. It doesn't always point to one exact location, but it narrows down the suspects significantly. For example, if the water stops at the base of the waterline tile or the bottom of the skimmer opening, it could indicate a horizontal bond beam crack behind the tile, a cracked skimmer body, or a failing skimmer pipe — all at roughly that same elevation.
Still not sure?
A diagnostic visit settles it.
When the bucket test is ambiguous or you see other warning signs, a specialist diagnostic visit is the definitive answer. Residential diagnostic starts at $360 and produces a written finding.
Common questions we hear.
"I keep topping off — should I let it drop to see where it stops?"
No. Although it is helpful information if the pool has already dropped and held at a certain level, intentionally letting it drop is risky. If the water level falls below the water table on the outside of the pool shell, it can create enough hydrostatic pressure to lift the shell out of the ground. Keep your pool filled and the water clean and clear while you wait for your appointment.
"My pool lost a lot and now it's stopped — did it fix itself?"
Usually, no — what happened is the water level dropped below the leak point. The leak is still there; it just can't leak water it can't reach. Once you refill, the loss returns.
The bottom line, briefly.
If your pool is losing water, the first question is never "where is it leaking?" — it's "is there actually a leak, or is this normal evaporation for the conditions I'm in?" The bucket test answers that question definitively in 24 hours. Once you know the answer, you know what to do next. If it's evaporation, no action needed — maybe a cover investment for the thirsty months. If it's a leak, a specialist can usually find and fix it faster than most pool owners expect.