Is My Pool Leaking or Just Evaporating? The Bucket Test

Your pool is down two inches and you are trying to work out whether that is a Texas August doing what a Texas August does, or whether something under the deck is quietly running your water into the ground. There is a definitive test for this, it costs nothing, it takes 24 hours, and almost nobody runs it before calling someone. Here is the test, plus how to read the answer well enough to point a technician at the right place.

What normal loss actually looks like here

A commonly used rule of thumb is a quarter inch of evaporation a day. That figure comes from milder conditions than ours. In a North Texas July, with afternoons near or past 100 degrees, low humidity, wind, and a deck radiating heat back at the water all evening, half an inch a day is ordinary and more than that is not remarkable.

Put that in gallons, because inches are what alarm people and gallons are what explain the water bill. A 15 by 30 foot pool has 450 square feet of surface. A quarter inch off that is about 70 gallons. Half an inch is about 140 gallons a day, near a thousand gallons a week, and none of it means anything is wrong.

Several things push that number up legitimately:

• Water features. A spa spillway, a waterfall, or a deck jet increases evaporation substantially, because it is atomizing water into hot dry air on purpose.
• Wind. An open, unfenced yard loses far more than a sheltered one. Wind strips the humid layer off the surface and lets the next batch evaporate.
• Heating. Warm water evaporates faster, and evaporation is the single largest route by which a heated pool loses its heat.
• Swimmers. Splash-out is real loss. A weekend with children in the pool moves a genuinely surprising amount of water onto the deck.
• Backwashing. If you have a sand or DE filter, every backwash sends pool water to waste by design. Cartridge filters do not do this.

The bucket test

This is the standard test, and it works because it puts a control sample of water in the same air, the same sun, and the same temperature as the pool. Whatever evaporation is doing to your pool, it is doing to the bucket.

1. Fill a clean five-gallon bucket with pool water to about an inch below the rim. Pool water, not hose water, so the temperature matches.
2. Set it on the second step of the pool so it is partly submerged and the water inside sits at roughly the same level as the water outside. Weight it with a brick if it wants to float. If your steps will not take it, the deck works, but the step is better because the temperatures match more closely.
3. Mark both levels.A strip of tape on the inside of the bucket at the water line, and a second mark on the outside of the bucket at the pool’s water line. A grease pencil on the tile works too.
4. Turn off the autofill and leave the pump on its normal schedule. Keep everything else exactly as it usually is.
5. Wait 24 hours, then compare. Do not swim, and if it rains hard, start over.
6. Read the result. Both dropped by the same amount means evaporation and your pool is fine. The pool dropped noticeably more than the bucket means you have a leak.

Reading where the leak is

A leak that behaves differently depending on whether the pump is running is telling you something specific about which part of the system is compromised.

That third column detail matters: where the water stops falling is where the leak is. Water only drains down to the level of the hole. If your pool loses six inches and then holds steady for days, look hard at whatever is at that depth. If it keeps going below every fitting, the leak is in the shell or in a main drain line.

Other things worth noticing

• Air in the system. Bubbles coming out of the returns, air collecting in the pump basket, or a pump that keeps losing prime all point to a suction-side leak, because the same defect that lets air in while running lets water out while off.
• A wet or unusually green patch in the yard. Underground plumbing leaks have to go somewhere. A strip of grass that stays lush through a drought is a clue.
• Settling or cracking deck. Water washing soil out from under a deck moves the deck.
• Puddles at the equipment pad. The easy case. Check the pump lid o-ring, the drain plugs, and the filter clamp before assuming anything is buried.
• Chemical demand that will not settle. Water that leaves takes its chemistry with it, and fresh fill water arrives with none. A pool that seems to eat chlorine and stabilizer for no reason is sometimes just a pool that is being partly replaced every week.
• The water bill. The most reliable early indicator most homeowners have, and the one they usually notice two months late.

Why leaks happen here specifically

North Texas is unkind to buried pool plumbing for two reasons that have nothing to do with build quality.

The first is our soil. Expansive clay swells when it takes on water and shrinks hard when it dries out, and it does both every year. That movement works on rigid PVC, on the joints between the shell and its fittings, and on the deck. It is the same soil behavior that cracks foundations across the Metroplex, applied to plumbing that nobody inspects.

The second is freeze damage, which shows up on a delay. Water left in a pipe or a fitting during a hard freeze expands and splits it, and often that split does not become a visible leak until the system is under pressure again in spring. A pool that started losing water in April is frequently a pool that was damaged in January. The prevention side of that is in our freeze protection guide, and it is the reason we push year-round circulation rather than closing a pool for winter here.

What you can check, and where it becomes our job

The bucket test, the pump-on versus pump-off comparison, the stop-level observation, and a walk around the equipment pad are all safely within reach and they are genuinely the most valuable information anybody will gather on this problem. Do those first.

A dye test is the next step and is also doable, with a caveat. With the pump off and the water perfectly still, a squirt of leak-finding dye near a suspected crack or fitting will get pulled into it visibly. The caveat is that it only works if you already know where to look and if the water is genuinely motionless, so it confirms a suspicion rather than finding one.

Past that point it becomes equipment work: pressure testing individual lines to find which one fails, listening equipment to locate a break under a deck, and pool-side inspection of skimmers, returns, and light niches. That is what our leak detection service is for, and it is worth saying plainly that arriving with your bucket test result already in hand makes it a shorter and cheaper visit.

One last piece of advice: do not let this ride. A leak does not stay the same size. Water moving through soil takes soil with it, which widens the path, which moves more water. The cheap version of this repair is the one done in the month you noticed it.