Why Is My Pool Losing Water? How to Tell Evaporation From a Leak

You walk outside, look at your swimming pool, and notice something isn't quite right. The water level is lower than it was a few days ago.

You add water with the garden hose, but a few days later, the level has dropped again.

Is your swimming pool leaking, or is the water simply evaporating?

It's a common concern for swimming pool owners, especially during hot summer months. While some water loss is perfectly normal, excessive water loss could indicate a leak that needs attention.

But there's another issue many pool owners overlook: Every time you add replacement water, you may also be adding minerals, metals, phosphates, and other dissolved substances that affect your pool chemistry.

Understanding where your water is going—and what's coming into your pool when you replace it—can save you money, reduce maintenance, and help prevent future water-quality problems.

How Much Water Does a Swimming Pool Normally Lose?

All outdoor swimming pools lose water through evaporation.

The amount depends on several factors, including:

• Temperature: Higher water temperatures generally increase evaporation.

• Humidity: Dry air allows water to evaporate more quickly.

• Wind: Moving air carries moisture away from the water's surface.

• Sun exposure: Direct sunlight heats pool water and contributes to evaporation.

• Water features: Fountains, waterfalls, and spillways increase the water's exposure to air.

• Pool covers: A properly fitted cover can significantly reduce evaporation.

Under many conditions, an uncovered swimming pool may lose approximately ¼ inch of water per day, although actual losses vary considerably. During hot, dry, or windy weather, evaporation can exceed ½ inch per day.

That might not sound like much, but consider what it means for a typical backyard swimming pool.

How Much Water Is Actually Evaporating?

Let's assume you have a rectangular swimming pool measuring 15 feet wide by 30 feet long.

That's 450 square feet of exposed water surface.

If the pool loses ¼ inch of water per day:

450 square feet × 0.0208 feet = 9.375 cubic feet of water

Since one cubic foot contains approximately 7.48 gallons:

9.375 × 7.48 = approximately 70 gallons per day

That means your swimming pool could lose:

• 70 gallons per day

• 490 gallons per week

• Approximately 2,100 gallons per month

And that's from evaporation alone.

During especially hot, windy weather, water losses could be substantially higher.

For homeowners, this means hundreds or even thousands of gallons of replacement water may enter the pool each month without an actual leak.

How Can You Tell Whether Your Pool Is Leaking?

Fortunately, there's a simple test that almost any homeowner can perform without specialized equipment.

It's called the bucket test, and it's one of the easiest ways to distinguish normal evaporation from a possible swimming pool leak.

The Swimming Pool Bucket Test

Step 1: Fill a bucket with pool water.

Use a clean five-gallon bucket and fill it approximately halfway to three-quarters full.

Step 2: Place the bucket on a pool step.

Position the bucket where it will remain stable, with the water inside the bucket near the same level as the surrounding pool water.

Make sure the bucket cannot tip over or float away.

Step 3: Mark both water levels.

Mark the water level inside the bucket and the pool water level on the outside of the bucket.

Step 4: Wait approximately 24 hours.

Avoid swimming, splashing, backwashing, or adding water during the test. Choose a period without rain if possible.

For a pool with an automatic water-level controller, temporarily disable the autofill so it doesn't replace water during the test.

Step 5: Compare the water loss.

If the water inside the bucket and the pool dropped by approximately the same amount, evaporation is the likely explanation.

If the swimming pool dropped significantly more than the bucket, you may have a leak.

For additional troubleshooting, repeat the test with the circulation pump off, provided doing so is safe for your equipment and water quality. A difference between pump-on and pump-off results can help a pool professional narrow down the possible source.

Important: The bucket test is a screening tool, not a definitive leak diagnosis. Rain, wind, splashing, and differences in exposure can affect the results.

Common Signs Your Swimming Pool May Have a Leak

Beyond the bucket test, there are several warning signs that may indicate a swimming pool leak.

1. You're Constantly Adding Water

If you're adding water every day or repeatedly running a garden hose to maintain the proper level, investigate whether the loss exceeds normal evaporation.

2. Wet Spots Around the Pool

Unexplained wet soil, soggy landscaping, or unusually green patches of grass near the pool could indicate leaking underground plumbing.

3. Air Bubbles in the Return Jets

Air entering the circulation system can indicate a problem on the suction side of the plumbing, although low water levels, loose pump lids, and other equipment issues can produce similar symptoms.

4. Cracks or Damage to the Pool Structure

Cracks in plaster, fiberglass, tile, or surrounding concrete may warrant inspection, particularly if accompanied by unexplained water loss.

Not every visible crack causes a leak, but structural movement should not be ignored.

5. Your Water Level Stops Dropping at a Particular Point

If the water repeatedly drops to the same level and then stabilizes, that may help identify a leak near a skimmer, return fitting, light niche, or another penetration.

6. Higher-Than-Normal Water Bills

An unexplained increase in water consumption may indicate that a pool leak or malfunctioning autofill system is wasting water.

Where Do Swimming Pools Commonly Leak?

Leaks can develop in several locations, including:

• Skimmers and their connections

• Return fittings

• Underground plumbing

• Pump and filter connections

• Equipment seals and valves

• Pool lights and niches

• Main drains

• Vinyl liners

• Fiberglass fittings or damaged surfaces

• Plaster cracks

• Water-feature plumbing

One often-overlooked source of water loss is the filter backwash or waste line.

A malfunctioning multiport valve can allow water to escape through the waste line while the filtration system is operating.

Before assuming you have an expensive underground leak, inspect the equipment pad and accessible plumbing for visible water loss.

If the bucket test suggests a leak but the source isn't obvious, a qualified pool leak-detection professional can perform more advanced testing.

Here's What Many Pool Owners Don't Realize: Replacing Water Changes Your Pool Chemistry

Whether water loss comes from evaporation or a leak, maintaining the proper water level often requires adding fresh water.

And that replacement water isn't necessarily chemically neutral.

Depending on the source, municipal or well water may contain:

• Calcium

• Magnesium

• Iron

• Manganese

• Phosphates

• Silica

• Dissolved salts

• Alkalinity

• Other minerals and dissolved substances

These constituents can affect pool chemistry, water clarity, staining, scale formation, and maintenance requirements.

The source of your replacement water matters.

Evaporation Can Concentrate Minerals in Your Pool

Here's an important distinction.

When pool water evaporates, primarily water molecules leave the pool. Most dissolved minerals and salts remain behind.

When you replace that evaporated water with tap or well water, you introduce additional dissolved minerals.

Over time, this process can increase calcium hardness and total dissolved solids (TDS).

For example, suppose your fill water contains 200 parts per million (ppm) of calcium hardness.

Every time you replace evaporated water, you're introducing more calcium.

Unlike water lost through evaporation, that calcium generally remains in the pool unless it's removed through water replacement, precipitation, or another treatment process.

Over months or years, calcium levels may climb high enough to contribute to:

• Scale on tile and pool surfaces

• Calcium deposits in heaters

• Scaling on saltwater chlorine generator cells

• Cloudy water

• Increased maintenance

This is particularly important in areas with naturally hard municipal or well water.

A Leak Creates a Different Problem

When water escapes through a leak, dissolved minerals leave with it.

Therefore, replacing leaked water does not necessarily cause the same mineral concentration effect as replacing evaporated water.

However, continuous water replacement can still change the pool's chemistry toward that of the incoming source water.

A leak may also increase the consumption of pool chemicals because treated water is continually being lost and replaced.

This distinction matters when diagnosing changes in calcium hardness, stabilizer, salt concentration, and other water-quality parameters.

Can Your Tap Water Introduce Phosphates Into Your Pool?

Yes, and this is a problem that many pool owners never consider.

Some municipal water utilities add phosphate-based compounds to drinking water as corrosion inhibitors.

These treatments help control corrosion within municipal distribution systems and household plumbing.

However, phosphates can also enter swimming pools through replacement water.

Phosphorus is an essential nutrient for algae, and orthophosphate is one form that algae can use.

While phosphates alone do not cause algae blooms in a properly maintained, adequately sanitized swimming pool, elevated phosphate concentrations can contribute to algae growth when other conditions allow it.

If you're continually replacing water with phosphate-containing municipal water, you may also be continually introducing this nutrient.

That's why treating phosphates without understanding their source can become a frustrating and expensive cycle.

What About Iron and Manganese in Well Water?

Homeowners who fill swimming pools with well water may face additional challenges.

Iron and manganese can be present in groundwater in dissolved forms that aren't immediately visible.

When these metals oxidize or precipitate, they can cause:

• Brown or reddish stains

• Black or dark-colored deposits

• Discolored water

• Deposits on pool surfaces

• Filter loading and maintenance problems

If your swimming pool repeatedly develops stains after adding fresh water, the problem may originate with your well rather than your pool equipment.

Testing the fill water before adding large quantities can help identify potential problems.

Why Does My Pool Need More Chemicals When I'm Constantly Adding Water?

Consider what happens when you continually replace treated swimming pool water.

Depending on whether water is lost through evaporation, leakage, backwashing, or splash-out, you may need to replenish or rebalance:

• Sanitizer

• Cyanuric acid (stabilizer)

• Salt

• Alkalinity

• Calcium hardness

• pH-adjusting chemicals

Evaporation itself does not significantly remove stabilizer or salt, but leaks, backwashing, splash-out, and draining remove water containing these dissolved substances.

This distinction is important.

If your pool is continually losing treated water through a leak, you're not simply wasting water.

You may also be losing money on the chemicals you've already purchased.

Can Copper Ionization Help Reduce Pool Maintenance?

Copper ionization offers an alternative approach to algae control that can help reduce dependence on certain traditional pool chemicals.

Unlike chlorine, which is consumed through reactions with contaminants and can be degraded by sunlight, copper ions provide a persistent residual in swimming pool water.

When maintained at appropriate concentrations, copper ions can help suppress algae growth.

This can be particularly valuable for pool owners who experience recurring algae problems or want to reduce reliance on chemical algaecides.

However, copper ionization does not prevent evaporation, repair leaks, remove dissolved minerals, or eliminate the need for proper filtration, water balance, oxidation, and required disinfection.

Copper concentrations must also be monitored and controlled. Excessive copper can contribute to staining, particularly when water chemistry is poorly managed.

And just like other dissolved minerals, copper remains in the water during evaporation but can be lost when pool water physically escapes through a leak or is drained.

The goal is not to replace one maintenance problem with another. It's to create a more efficient and manageable water-treatment system.

How to Reduce Swimming Pool Water Loss

Although evaporation cannot be eliminated entirely, there are practical ways to reduce unnecessary water consumption.

Use a pool cover. A properly fitted cover can dramatically reduce evaporation, especially during periods when the pool isn't being used.

Limit unnecessary water features. Waterfalls, fountains, and spillways can increase evaporation by exposing more water to moving air.

Inspect your pool equipment regularly. Small plumbing leaks and malfunctioning valves can waste significant amounts of water over time.

Maintain the correct water level. Overfilling the pool may cause unnecessary water loss through overflow systems or splash-out.

Monitor water consumption. Periodically measure the water level or track autofill usage to identify unusual changes.

Test your source water. Knowing what's in your municipal or well water can help you anticipate chemical changes caused by refilling.

Repair leaks promptly. Even a relatively small leak can waste thousands of gallons over time.

The Bottom Line: Know Where Your Water Is Going and What's Coming Back In

If your swimming pool is losing water, don't immediately assume something is broken.

Evaporation is a normal part of owning an outdoor pool, especially during hot, dry, or windy weather.

But excessive water loss deserves investigation.

Start with the bucket test. Inspect the equipment. Look for signs of leaking plumbing or structural damage.

And remember that the water you add to replace what's been lost can have a significant effect on your pool's chemistry.

Evaporation removes water but leaves most dissolved minerals behind. Leaks remove both water and dissolved substances. Understanding the difference can help you avoid unnecessary chemical treatments and maintenance costs.

At Intec America, we believe better swimming pool maintenance begins with understanding water chemistry—not simply adding more chemicals whenever a problem appears.

With more than 50 years of experience in water-treatment and copper ionization technologies, Intec America offers solutions designed to help pool owners maintain cleaner water while reducing dependence on traditional chemical treatments.

If you're looking for a smarter approach to swimming pool water treatment, learn more about our copper ionization systems at IonizedPool.com or visit Intec America.

Because maintaining a swimming pool should be about enjoying the water—not constantly fighting its chemistry.