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Water loss in open-surface swimming pools is a far more complex process than it might seem. These losses stem from various physical and operational factors, most notably evaporation and filter backwash procedures.
In particular, environmental factors such as solar radiation, wind speed, air temperature, relative humidity, and pool surface area directly govern the rate at which water evaporates. Alongside these, the frequency and duration of filtration backwashing represent the primary operational driver of water consumption.
Therefore, accurately analyzing pool water loss requires evaluating climatic conditions, pool design, and daily operational habits together, rather than relying on isolated parameters like temperature alone. This holistic approach yields the soundest outcomes for both energy efficiency and sustainable water management.
Under normal summer atmospheric conditions (25-35°C, 40-60% humidity), normal pool evaporation ranges between 4 mm and 8 mm per day (approx. 200-400 L/day on a 50 m² pool). Water loss exceeding 10-12 mm daily indicates a structural crack or plumbing leak, verifiable using a 24-hour static bucket test.
Water loss in open-surface pools primarily stems from evaporation and backwash procedures. Solar radiation, wind, temperature, humidity, and surface area drive evaporation, while filter cleaning frequency and duration determine operational losses. Accurate analysis requires evaluating both climate factors and operating habits simultaneously.
Using the calculation tool below, you can effortlessly calculate the daily and annual water loss caused by evaporation and backwashing in your pool.
Is your pool's water level constantly dropping without you being able to fully understand why? Especially during the hot summer months, many pool owners ask themselves, "Is my pool leaking?"
Yet in most cases, this drop is not caused by a leak worth panicking over, but by evaporation — a completely natural process. Factors such as air temperature, wind, humidity, and hours of sunlight can cause pool water to decrease faster than expected.
In this article, we will help you understand the real cause of your water loss by examining, step by step, the differences between evaporation and leakage, simple test methods, and the correct solution recommendations.
Evaporation is the process by which water turns from its surface into a gas and escapes into the atmosphere, and it is one of nature's most fundamental physical cycles. Although invisible, this phenomenon is one of the most important causes of water loss, especially in open-surface pools.
The evaporation rate is directly affected by many environmental factors such as solar radiation, air temperature, wind speed, relative humidity, and the width of the water surface. On sunny days, the water surface heats up, its molecules gain speed, and with this increase in energy, water turns into gas and mixes into the atmosphere.
Wind accelerates evaporation even further because it continuously carries away the moist air layer that forms at the surface, making it easier for new molecules to escape into the atmosphere. Likewise, low humidity also increases evaporation, because dry air absorbs water vapor more quickly.
As a result, it is entirely normal for pool water to decrease by a few millimeters or even centimeters through evaporation, especially during the summer months and in dry climate regions. However, if not regularly monitored, these natural losses can turn into a significant amount of water and energy waste in the long run.
On average, a daily water loss of 5–12 mm is normal in an open-surface pool. For a 100 m² pool, this translates into hundreds of m³ of water per year.
The most practical answer to this question is found with the "bucket test." This easy-to-apply test clearly reveals the cause of the water loss.
This test should be done in a calm environment without wind and without direct sunlight. The results give a fairly clear picture within 24 hours.
The evaporation rate varies according to climate conditions:
| Air Temperature (°C) | Average Evaporation (mm/day) |
|---|---|
| 0 – 20 °C | ≈ 3 mm/day |
| 20 – 30 °C | ≈ 6 mm/day |
| 30 – 40 °C | ≈ 9 mm/day |
| Above 40 °C | ≈ 12 mm/day |
These values can translate into a total annual water loss of 300–500 m³ from the pool surface.
If the bucket test result shows that the pool water has dropped more, this may indicate a leak or connection problem. Expert inspection is required in the following situations:
With professional waterproofing inspection, you can minimize both water loss and energy costs.
A drop in your pool's water level does not always mean a malfunction or a leak; in most cases, especially in hot, dry, and windy climates, this is entirely due to a natural process called evaporation. Sunlight and wind accelerate the molecules on the water's surface, causing them to mix into the atmosphere, which can create a visibly noticeable level of water loss. What matters, however, is being able to correctly distinguish between evaporation and a possible leak. To do this, you can apply the simple yet effective bucket test, observe the water level over a few days, and seek support from an expert whenever in doubt. Thanks to accurate analysis and regular maintenance, you can make your pool's water management more efficient, prevent unnecessary water waste, and significantly reduce maintenance costs in the long run.
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Under normal summer atmospheric conditions (25-35°C air, 40-60% relative humidity), normal pool evaporation ranges between 4 mm and 8 mm per day, which corresponds to roughly 200-400 liters on a 50 m² pool. Losses above this range should be examined carefully.
The most reliable method is a 24-hour bucket test. A water-filled bucket is placed on the pool edge and the water levels of both the pool and the bucket are marked. A drop in the bucket reflects evaporation only, while a drop in the pool reflects evaporation plus any leak; the difference between the two indicates the leak.
Daily water loss exceeding 10-12 mm indicates a structural crack or plumbing leak and should be confirmed with a 24-hour bucket test. Losses above this threshold require expert inspection.
Filter backwashing typically consumes 150-300 liters per minute over a 2-3 minute cycle. This is a normal part of standard filtration operation, but backwashing more frequently than necessary significantly increases total water loss.
Using a thermal/solar pool cover can reduce evaporation-related water loss by 90-95%. Keeping the cover closed during unused night hours in particular saves both water and heating energy.
Wind speed, low humidity, a large water-to-air temperature difference, heavy bather traffic, equipment that creates water movement such as jacuzzis or fountains, and overly frequent backwashing are the main factors that increase evaporation and total water loss.
Using a pool cover, installing windbreak planting or panels, keeping water level and temperature within the optimum range, adjusting backwash frequency based on the filter's dirt indicator, and regular leak inspections are the primary measures that minimize water loss.
Instantly calculate your loss using our water loss calculation tool, or contact our team for professional waterproofing and leak detection.