If your pool water level keeps dropping, it’s usually caused by evaporation, splashing, equipment issues, or a leak. The key is figuring out which one is happening. Some loss is completely normal, but excessive water loss can signal a problem that needs attention. Let’s break down the most common reasons.
1. Normal Evaporation
Evaporation is the most common cause of water loss, especially during hot, dry, or windy weather.
Typical evaporation rates:
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¼ to ½ inch per day in warm climates
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Higher when temperatures are high and humidity is low
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Increased if the pool is heated or uncovered
You may notice more evaporation when:
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Temperatures rise quickly
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The pool heater is running
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Wind blows across the water's surface
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The pool sits in direct sunlight most of the day
Quick tip: Using a pool cover when the pool isn’t in use can dramatically reduce evaporation.
2. Splash-Out and Swimmers
Every cannonball removes a little water.
Pools lose water from:
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Kids jumping or playing
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Water features like waterfalls or deck jets
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Heavy pool activity or pool parties
While splash-out usually isn’t huge, frequent swimming can lower the water level noticeably over time.
3. Backwashing or Filter Maintenance
If you have a sand or DE filter, water is intentionally discharged during backwashing.
Water loss may happen if:
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Backwashing occurs frequently
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The backwash valve leaks slightly
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The multiport valve isn’t fully sealing
This can sometimes drain several inches at once, depending on how long the backwash cycle runs.
4. Plumbing or Equipment Leaks
Sometimes water loss comes from pool equipment or plumbing.
Common culprits include:
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Pump lid O-ring leaks
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Filter tank cracks
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Loose unions or fittings
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Leaking valves
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Underground plumbing line leaks
Check around your equipment pad for:
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Wet soil
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Constant dripping
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Air bubbles in the pump basket
If the equipment area is always damp, that’s a strong clue.
5. Structural Leaks in the Pool
If the pool shell itself is leaking, water may escape through:
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Skimmer cracks
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Return line fittings
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Light niches
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Vinyl liner tears
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Cracks in concrete or fiberglass
Signs of a structural leak:
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Water loss greater than 1 inch per day
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The pool stops losing water at a certain level
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Wet spots around the pool deck or yard
6. The Simple “Bucket Test”
A quick way to tell if it’s evaporation or a leak is the bucket test.
How to do it:
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Fill a bucket with pool water.
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Place it on a pool step so the water inside matches the pool level.
- Mark the water line inside the bucket and on the pool wall.
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Wait 24 hours with the pump running normally.
Results:
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If the pool loses more water than the bucket, you likely have a leak.
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If they drop about the same amount, it’s probably evaporation.
When to Investigate Further
You should look deeper if:
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Water drops more than 1 inch per day
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You’re refilling the pool every couple of days
- The water level stops dropping at a specific point
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You see soggy ground around the pool or equipment
Pro Tip: Keeping the water level around the middle of the skimmer helps your pump run efficiently and prevents air from entering the system.
Bottom line:
Most pools lose some water naturally, but excessive or consistent loss usually means a leak somewhere in the system. Starting with the bucket test and a quick equipment check can help you narrow it down fast.
