Pool Losing Water? How to Tell Evaporation From a Leak in Arizona

Almost every homeowner asks us the same question at some point in the summer: is my pool losing water because of the heat, or do I have an actual leak? In the East Valley the answer isn't obvious just by looking at the water line, because our climate produces evaporation rates that would look alarming almost anywhere else in the country. The good news is you can tell the difference yourself in about 48 hours, and it doesn't cost anything but a bucket.

How much water loss is actually normal here

Evaporation in an Arizona summer is aggressive. Between intense heat, low humidity, direct sun, and wind across an open surface, a pool can commonly lose somewhere in the range of a quarter to half an inch of water a day during peak summer months — more if you run a spa spillover, a water feature, or the pool sits in a particularly windy or sun-exposed part of the yard. That adds up fast: a half inch a day is roughly three and a half inches a week, which is enough to make a homeowner who hasn't dealt with it before assume something is wrong. Often nothing is. The trick is separating expected evaporation from an actual leak, and evaporation and leaks behave differently enough that a simple test can usually tell them apart.

The bucket test, step by step

This is the standard, low-cost way to isolate the problem, and it's worth doing before you call anyone out for a leak inspection:

• Fill a bucket with pool water and set it on the second or third step of the pool, so it's partially submerged and exposed to the same sun and air as the pool itself.
• Mark the water level inside the bucket and the water level of the pool on the outside of the bucket, using tape or a permanent marker, at the same time.
• Run the pool normally with the pump on its usual cycle for 24 hours, then compare the two marks. If the pool line has dropped noticeably more than the bucket line, you're likely losing water through the plumbing while the pump is circulating.
• Reset both marks and repeat the test with the pump switched off for 24 hours. If the pool now drops in line with the bucket, or close to it, evaporation is probably your main culprit and there's no leak to chase.

Because the bucket loses water only to evaporation, any extra drop in the pool beyond what the bucket shows is water going somewhere else — and comparing the pump-on and pump-off readings tells you roughly where.

What the pump-on vs. pump-off comparison tells you

This is the part most homeowners miss, and it's the most useful diagnostic step in the whole process. If the pool loses noticeably more water while the pump is running than while it's off, that points toward a pressurized-side leak somewhere in the plumbing — a cracked union, a failing pump seal, a loose fitting at the filter or heater, or a break in a return line that only leaks under pump pressure. If the loss looks roughly the same whether the pump is on or off, and it's in the same range as the bucket, that's usually consistent with a leak in the pool shell itself, the skimmer, or a suction-side fitting that seeps slowly regardless of whether water is being pushed through it — or, in a lot of cases, it just confirms you're dealing with ordinary evaporation and nothing is actually wrong.

Other clues worth checking

The bucket test is the most reliable single tool, but a few other signs usually show up alongside a real leak:

• Wet spots, soft ground, or unusually green grass in one area of the yard near the equipment pad or plumbing runs, which can mean water is escaping underground before it ever reaches the pool surface.
• Air bubbling into the pump basket or visible in the return jets, which often means a suction-side fitting is pulling in air instead of water — a classic sign of a plumbing leak rather than evaporation.
• Cracks or gaps at the tile line, around lights, or where the deck meets the coping, which can indicate a structural leak in the shell itself.

Why autofill can hide a leak — and cost you twice

If your pool has an automatic fill valve, it's worth understanding what that convenience is actually doing. An autofill line quietly tops off the pool whenever the water drops below a set level, which means a real leak can run for months without you ever noticing a falling water line — the autofill is masking the symptom while the underlying problem keeps draining water and, often, money. You'll usually see it first on the water bill rather than at the pool.

There's a second cost that's easy to overlook: every gallon that autofill adds is fresh tap water, and East Valley tap water runs hard. Constant top-ups don't just replace lost volume — they steadily raise calcium hardness and total dissolved solids, since the minerals in that new water stay behind every time some of it evaporates again. A pool that's quietly autofilling to compensate for a hidden leak tends to scale up faster than one that only gets refilled occasionally, which is exactly the mechanism we cover in more depth in how to stop calcium buildup on your Arizona pool. If your autofill valve seems to be running more than it used to, that's often the first real clue something below the surface has changed.

When it's time to call a professional

If the bucket test points to a pump-side or plumbing leak, or you're seeing wet spots and air in the basket alongside water loss that outpaces what evaporation alone would explain, that's a job for a technician rather than more guessing. Pressurized-side leaks in particular can worsen quickly and are worth catching early before they damage equipment or erode the ground around your pad. Our equipment repair team can pressure-test the plumbing, inspect pump seals and fittings, and pin down exactly where water is escaping. If you're not sure which category your pool falls into after running the test, reach out and describe what you're seeing — we can usually tell you over the phone whether it sounds like normal summer evaporation or something worth a site visit.