Pool leak or evaporation?
How to know for certain.
Every Florida pool loses water every day — the question is whether yours is losing too much. Here's how to answer that in 24 hours, using nothing but a bucket and the professional protocol our technicians use in the field.
- On the Gulf Coast, normal evaporation is roughly 1/16″ to 1/4″ per day. A screened pool sits at the low end; a heated, unscreened pool in a winter cold front sits at the top.
- Losing more than 1/4″ a day — or a full inch — is almost always a real leak, not weather.
- The bucket test is the only reliable homeowner method, and most people run it wrong. The professional protocol below fixes that.
- If the test confirms a leak, don't let the water keep dropping — low water plus a high water table can lift a pool shell out of the ground.
- When and where the water stops dropping are the two most valuable clues you can give a leak specialist.
On Florida's Gulf Coast, your pool loses water to the sky all year round — only the reason changes with the calendar. On some days, losing a quarter-inch is completely normal, even though it looks and feels like a leak.
Summer heat drives the water temperature up and evaporation with it. Winter cold fronts pull dry, windy air across the surface and do the same thing from the opposite direction. Before you assume the worst — or shrug off a real problem — it pays to understand what's actually happening on the surface of your pool.
What drives evaporation
Evaporation comes down to three things: the gap between water temperature and air temperature, the humidity of the air sitting above the pool, and how quickly wind replaces that air with drier air. More heat in the water, drier air above it, and more breeze moving that air along — all push evaporation up. Here's how the factors stack up over a Tampa Bay pool:
Water temperature
Warmer water evaporates faster. A heated pool in January can out-evaporate an unheated pool in July.
Humidity
Dry air drinks more water. Our Gulf humidity usually slows evaporation — until a winter cold front strips it away.
Wind
Wind sweeps humid air off the surface and replaces it with dry air. The afternoon sea breeze that rolls in off the Gulf does exactly this, every day.
Sun exposure
Direct Florida sun heats the surface layer and accelerates loss. Shaded pools evaporate noticeably less.
Screen enclosure
A screened lanai — which most West Coast pools have — cuts wind and traps humidity. Screened pools typically evaporate 30–50% less than open ones.
Water features
Waterfalls, spillover spas, deck jets and bubblers multiply the water's surface area — and evaporation multiplies with it.
Pool cover
A solid cover can cut evaporation by 90% or more. Few Florida pools use one, but they work.
Swimming & splash-out
A pool party's worth of splash-out is real water loss, but it isn't a leak. Very common after a heavy-use weekend.
Typical Gulf Coast evaporation rates
For most pools from New Port Richey down to Venice, daily evaporation lands between 1/16 and 1/4 inch under normal conditions. The top of that range shows up on windy days, or when the water is much warmer than the air above it. Screened pools sit toward the bottom of the range. The only combination that pushes meaningfully past 1/4 inch is a heated, unscreened pool running through a windy cold front — which is uncommon, and temporary.
Rule of thumb
More than 1/4 inch per day, sustained over several days, deserves a bucket test. A full inch a day is a leak until proven otherwise.
How much water are you actually losing?
Inches are abstract; gallons are not. For a rectangular pool, gallons per inch equals length × width × 0.62. A few common sizes:
| Pool size | Gallons per inch of water |
|---|---|
| 14 × 28 | 244 gallons |
| 15 × 30 | 279 gallons |
| 16 × 32 | 318 gallons |
| 18 × 36 | 402 gallons |
| 20 × 40 | 496 gallons |
| 25 × 50 | 775 gallons |
Irregular and freeform shapes land at roughly 75–80% of the rectangular figure.
Quick check: your pool's gallons per inch
Enter your pool's length and width in feet.
When a homeowner in Sarasota tells us their 18×36 pool is "losing an inch a day," what they're really telling us is that roughly 400 gallons a day — over 12,000 gallons a month — is going somewhere it shouldn't. Even at the peak of a Florida summer, evaporation rarely exceeds a quarter-inch per day. A full inch is almost never the weather.
The bucket test: the professional protocol
Every other homeowner method involves guessing at evaporation rates. The bucket test doesn't guess. Because the bucket and the pool share identical weather, temperature, humidity and wind for the same 24 hours, their evaporation should match exactly. Any difference between the two is your leak, measured.
Most pool owners have heard of the bucket test. Almost nobody runs it the way a leak-detection technician would. The steps below are the actual field protocol our team uses — including the details that separate a reliable result from a misleading one.
Shut the system down
Turn the breaker off or put the equipment in service mode, with every body of water filled to its proper running level.
Isolate raised bodies of water
If you have an attached spa or fountain, siphon it down about an inch below its spillover lip so it can't trickle into the pool during the test. The same applies to negative-edge pools.
Valve off suction and return lines if you can
Point three-way valves "off" toward the higher body of water, and include solar plumbing. One caution from experience: valves that haven't been turned in years may not reseal once moved — if a valve looks ancient, leave it and just note it.
Fill and mark the bucket
Fill a 2–5 gallon bucket with pool water to within an inch of the rim. Mark the level with a fine pencil "Y": draw a diagonal line through the waterline, then a second line crossing it exactly at the water's surface. That intersection reads far more precisely than a fat marker stripe.
Place the bucket on the top step
It should sit at least half-submerged in the pool — this keeps the bucket water at pool temperature, which is critical — and get roughly the same sun exposure as the pool surface. No suitable step? Set it on a swim-out or weight it on a platform.
Mark the pool the same way
Mark the level on the tile or inside the skimmer with the same "Y" technique — on a long pool, mark the middle of the long side, where wave action distorts the least.
Wait 24 hours and compare
Don't swim, don't top off, don't touch the bucket. Levels should track within 1/16 inch per day of each other.
How to read your result
Both dropped the same
Evaporation only. No leak. Recheck in high season if the heavy drop recurs.
Pool dropped more than bucket
You have a leak — the difference between the marks is your leak rate. Time to call a specialist.
Bucket dropped more than pool
Something interfered — wind, a tipped bucket, or a bad mark. Re-run the test.
Have a spa or fountain? Read this
With multiple bodies of water, the result table changes: if the higher body dropped and the lower body didn't rise, you have a leak. But if the lower body came up while the higher one dropped, the problem is more likely a failed valve — a check valve or Jandy valve letting water flow backwards between bodies. That's a different (and usually cheaper) repair than a structural leak, and it's a distinction most DIY guides miss entirely.
Two edge cases worth knowing
Variable water features
If a waterfall or spillover runs on a timer, run the test with features on their normal schedule. Testing with everything off understates your real-world loss.
Intermittent leaks
Some leaks only open up under specific conditions: pump on, heater running, spa spilling. If repeated bucket tests contradict each other, that inconsistency is itself a clue — and a good reason to bring in detection equipment.
The Bucket Test Field Checklist (PDF)
Print it, take it poolside, and tick off each step of the professional protocol — including the spa/fountain interpretation table.
Free download — no email required.
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:
1 · A heater was just added
A new heater can double evaporation overnight. We take calls every winter from owners convinced the installer caused a leak — usually it's just heated-pool physics.
2 · A screen enclosure came down
After a storm or renovation, an unscreened pool can evaporate at double its old rate. The "leak" started the day the screen came down — not a coincidence, but not a leak either.
3 · A new water feature went in
Waterfalls and bubblers add surface area, and surface area is evaporation. A "leak" that appeared right after a remodel is often the features doing what features do.
4 · A vacation home just emptied out
Rental guests splash out a surprising amount of water. The level drop you find on inspection day often left the pool one cannonball at a time.
5 · The season changed
Warm water under cooler, drier, windier air evaporates fast — that's every Gulf Coast autumn. A pool that held steady all summer can start visibly dropping in November without a single new problem.
When the bucket says evaporation, but it doesn't feel right
The bucket is usually right. The legitimate exceptions: the bucket sat in shade while the pool baked in sun (or vice versa) — placement must match the pool's average exposure. Or the difference is within 1/16-inch marking error, which is the honest noise floor of the method. Leaks that small exist, but they're rare — and they're exactly what a professional diagnostic is for.
Test says leak — what your pool is telling you
The pattern of loss is diagnostic gold. Before you call anyone (including us), note which of these fits — it will make the detection visit faster and sharper:
| Loss pattern | What it points to |
|---|---|
| Only while the pump runs | The pressure side: pad equipment (a failed D.E. waste valve, a weeping filter union), solar panels that only pressurize when the pump is on, or a spa pushed above a crack that sits dry at rest. |
| Only while the pump is off | Classic suction-side pipe break: while running it sucks air instead of leaking water, then bleeds out at rest. Can also be a spa siphoning back into the pool and out an overflow. |
| Same loss either way | Structural or waterproofing: shell cracks, bond-beam cracks behind the tile, a leaking light niche, a cracked skimmer body. |
| Loss stops at a specific level | The single most useful clue there is. Water finds its own level — where it stops is roughly where the leak lives. Note the exact level and tell your technician. |
One warning worth repeating
Never intentionally let your pool keep draining to "see where it stops." If the water inside falls below the water table outside the shell, hydrostatic pressure can lift the entire pool out of the ground. Keep it topped up and the water clean while you wait for your appointment.
Common questions we hear
How much evaporation is normal for a pool in Tampa Bay?
How do I tell if my pool is leaking or just evaporating?
How many gallons is an inch of water on my pool?
Should I let my pool keep draining to find the leak?
My pool was losing a lot, then it stopped. Did it fix itself?
What does professional leak detection cost in Tampa Bay & Sarasota?
Bucket test came back positive?
Our technicians find leaks without draining your pool, deliver a written report 2–3× more detailed than the industry standard, and back every diagnosis with a 60-day written warranty. Detection from $360 across Tampa Bay, St Pete and Sarasota.