Proclearpools.com |Why Is My Pool Losing Water Only When the Pump Is Running?

Why Is My Pool Losing Water Only When the Pump Is Running?

You fill your swimming pool to its normal level, turn on the equipment and go about your day.

By the next morning, the water level has dropped noticeably.

But when the pump is off for an extended period, the water doesn’t seem to disappear as quickly.

In Lake Havasu City, Bullhead City and Fort Mohave, evaporation is an everyday concern. However, water loss that changes significantly depending on whether the pump is operating may indicate a plumbing or equipment problem.

If your pool loses substantially more water while the pump runs, a leak on the pressure side of the circulation system is one possibility. The return plumbing, filter connections, equipment fittings and other pressurized components may need inspection.

The important first step is determining whether the difference is real and repeatable.

Why Does Running the Pump Change Water Loss?

Your pool’s circulation system moves water through two main sections.

The suction side carries water from the pool toward the pump. The pressure side carries water from the pump through the filter and other equipment before returning it to the pool.

When the pump operates, pressure increases in the return-side plumbing.

If a pipe, fitting or equipment connection has a leak, that pressure may cause water to escape more rapidly.

When the pump shuts off, the pressure disappears, and the leak may slow or stop.

However, the exact behavior depends on the leak’s location, plumbing elevation and other conditions.

1. A Return-Line Leak May Be Responsible

Return lines carry filtered water back to the swimming pool.

Some return plumbing runs underground between the equipment pad and the pool shell.

A damaged pipe or fitting can allow water to escape into the surrounding soil.

Because the leak may be buried, you might not see a puddle.

Possible warning signs include:

• Water loss that increases when the pump operates
• Repeatedly needing to add water
• Unexpected damp areas near the pool or equipment
• Soil movement or settling near underground plumbing
• Changes in circulation performance

None of these signs proves that a return line is leaking, but together they may justify professional testing.

ProClear Pools offers pool plumbing repairs and supplies for homeowners in Mohave County.

2. Check for Leaks Around the Equipment Pad

Not every leak is underground.

Water may escape from accessible equipment connections, including:

• Filter housings and fittings
• Pump discharge connections
• Valve assemblies
• Heater plumbing connections
• Unions and threaded fittings
• Damaged or deteriorated seals

Look for water accumulating near the equipment pad while the system operates.

In Arizona’s dry climate, small leaks can evaporate quickly, so mineral deposits or persistent dampness may provide clues.

Observe the equipment without opening pressurized components or reaching near electrical connections.

Never attempt to tighten or disassemble a leaking pressurized filter while the pump is operating.

3. Could the Pool Filter Be Leaking?

Yes.

Filters operate under pressure, and damaged seals, housings, valves or connections may allow water to escape.

A filter that leaks only while the pump runs can produce a noticeable difference in water loss.

Inspect the outside of the filter for visible moisture, drips or mineral deposits.

If the filter housing is cracked or damaged, turn the equipment off and arrange professional service.

Pressurized pool filters can be hazardous when damaged or improperly serviced.

ProClear provides pool filter cleaning, repair and replacement services for residential pool systems.

4. Don’t Overlook the Waste or Backwash Line

Some filtration systems have a multiport or backwash valve that directs water to a waste line during cleaning.

If a valve seal or internal component fails, water may continue flowing toward the waste line even when the system is set to normal filtration.

Depending on how the waste plumbing is installed, the water may discharge somewhere that isn’t immediately visible from the pool.

This can create substantial water loss while the pump operates.

If your system has a waste or backwash line, have it checked for unintended flow during normal operation.

5. Could It Still Be Evaporation?

Yes. Evaporation must be considered before assuming there’s a leak.

Lake Havasu’s hot temperatures, low humidity, wind and exposed pool surfaces can contribute to significant evaporation.

Evaporation occurs whether the circulation pump is running or not.

However, water features, spillways, aeration and increased surface disturbance can change evaporation rates during pump operation.

That means higher water loss while the pump runs doesn’t automatically prove a broken pipe.

Check whether waterfalls, fountains or other features operate only when the pump is on.

How Do You Perform a Pool Bucket Test?

A bucket test can help compare pool water loss with evaporation under similar conditions.

Use a clean bucket and follow these general steps:

1. Fill the pool to its normal operating level.
2. Place a bucket on a stable pool step where it won’t tip over.
3. Add pool water to the bucket until the water level inside is reasonably close to the surrounding pool water level.
4. Mark the water level inside the bucket and the pool water level outside it.
5. Allow the test to run for approximately 24 hours under safe, normal conditions.
6. Compare the amount of water lost from the pool with the amount lost from the bucket.

If the pool loses substantially more water than the bucket, a leak becomes more likely.

To compare pump-on and pump-off conditions, separate tests may be useful. Keep weather conditions and water features as consistent as practical.

Don’t disable necessary circulation or sanitation for an extended period simply to perform a test. Follow equipment guidance and obtain professional help if needed.

What If the Pool Loses More Water When the Pump Is Off?

That pattern may point toward a different type of problem.

For example, certain suction-side plumbing leaks can behave differently when the pump isn’t running.

Water may also escape through a leak in the pool shell, a fitting or another location unrelated to pump pressure.

Water loss patterns are diagnostic clues, not definitive proof of where a leak exists.

Professional testing may be necessary to isolate the affected plumbing or structure.

Can a Pool Leak Damage Your Yard or Deck?

Yes.

Water escaping underground can affect surrounding soil and potentially contribute to settlement, erosion or damage to nearby structures.

Not every pool leak causes structural damage, but prolonged water loss shouldn’t be ignored.

If you notice new cracks, sinking pavers, persistent wet spots or unusual soil movement, arrange an evaluation promptly.

Should You Keep Running a Pool With a Suspected Leak?

That depends on the severity and location of the problem.

If water is leaking near electrical equipment, the pump cannot maintain prime or the water level is approaching the skimmer opening, shut down the affected equipment and seek qualified service.

Continuing to operate a pump without adequate water can damage the equipment.

Even when the leak appears minor, repeatedly replacing lost water can increase water costs and make maintaining balanced pool chemistry more difficult.

Frequently Asked Questions

Why does my pool lose water only when the pump is on?

A pressure-side plumbing or equipment leak is one possibility. Water features and other circulation-related conditions can also increase evaporation or water loss.

Can a pool filter leak only while the pump runs?

Yes. Filter housings, seals, valves and connections operate under pressure and may leak more noticeably when the pump is running.

How can I tell evaporation from a pool leak?

A bucket test compares water loss from the pool with water loss from a nearby container exposed to similar weather conditions.

Can a pool leak be underground without a wet spot?

Yes. Underground water may drain into surrounding soil without producing an obvious puddle at the surface.

Will a pool leak stop when I turn off the pump?

Some pressure-side leaks may slow or stop when the pump is off. Other leaks can continue regardless of pump operation.

Find the Cause Before You Keep Adding Water

If your pool loses more water while the pump runs, don’t assume it’s normal Arizona evaporation.

Check accessible equipment for visible leaks, review water-feature operation and consider a controlled bucket test.

ProClear Pools provides pool plumbing and equipment repairs along with professional pool service throughout Lake Havasu City, Bullhead City, Fort Mohave and surrounding Mohave County communities.

To discuss unexplained pool water loss or equipment problems, contact ProClear Pools for service options.