How to Tell If Your Pool Has a Leak — and What to Do About It

Pool water naturally evaporates — but if you’re constantly topping up the water level or noticing soggy patches around the pool, you could be dealing with a leak. The problem is, pool leaks can be sneaky and often hard to spot.

In this guide, we’ll show you how to detect a pool leak, common causes, and what to do next — whether it’s a DIY fix or time to call in a pro.

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Is It a Leak or Just Evaporation?

Before you panic, understand how much water loss is normal.

✅ Typical evaporation:

• 2–5mm per day in warm, dry weather

• Up to 7mm per day with wind and high temps

• Slightly more if the pool is heated or uncovered

🚩 Signs it might be a leak:

• More than 25mm (1 inch) lost in 24 hours

• Air bubbles coming from return jets

• Constantly wet soil or pooling around the pool

• Cracks or tiles shifting in the shell

• Equipment losing prime or sucking air

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Step 1: Do the Bucket Test

The easiest DIY test to confirm if your pool is leaking.

What you’ll need:

• A bucket

• A permanent marker or tape

• Water

How to do it:

1. Fill a bucket with pool water to about 5cm from the top.

2. Place the bucket on the pool step so it’s partially submerged.

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

4. Turn off the pool pump and leave it for 24 hours.

Results:

• If the pool water drops more than the bucket water, you have a leak.

• If both levels drop evenly, it’s just evaporation.

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Step 2: Check for Leaks at the Equipment

Look at the pump, filter, chlorinator and pipework.

Look for:

• Damp concrete or puddles

• Salt stains or white crust (calcium deposits)

• Air in the pump basket or bubbles in returns

Fixes might be as simple as tightening unions or replacing O-rings — most of which are available in our pool products section.

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Step 3: Inspect the Pool Shell

Surface cracks and loose tiles can be clues.

Check for:

• Fine cracks in plaster, fibreglass or tiles

• Loose skimmer edges or returns

• Bubbling in the paint or fibreglass

Use a dye test: squirt a few drops of coloured pool dye near suspected cracks while the water is still. If the dye is drawn in, it could be a leak.

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Step 4: Examine the Skimmer and Returns

The skimmer box and return fittings are common leak spots, especially in older pools.

What to check:

• Cracks inside the skimmer box

• Loose or shifting skimmer collars

• Gaps around return fittings

Leaks in these areas can often be sealed with a pool-safe epoxy or underwater sealant.

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Step 5: Rule Out the Backwash Line

A leaking multiport valve can send water down the backwash line constantly.

Test it:

• Turn off the pump and check the backwash outlet

• If water continues to trickle, the valve may need repair

Backwash line leaks are common — and easy to overlook.

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Step 6: Monitor Water Loss with the Pump On vs Off

If your pool loses more water when the pump is running:

• It could be a pressure-side leak (after the pump)
  If the water loss slows when the pump is off:

• It may be a suction-side leak (before the pump)

This helps narrow down the area of the leak.

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Step 7: Check Around Pool Lights

If you have underwater lighting, inspect the conduit pipe that connects the niche to the power source.

Warning signs:

• Water around the light fitting

• Movement or cracks near the housing

These often require professional inspection, especially with electrical components involved.

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Step 8: When to Call a Leak Detection Specialist

Call in the pros if:

• You’ve done the tests and still can’t find the leak

• The leak is behind walls, under paving, or inside plumbing

• There are signs of structural damage or heavy water loss

Leak detection tools include pressure testing, electronic sensors, and acoustic listening devices.

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What to Do While Waiting for Repairs

• Keep water above the skimmer opening to avoid pump damage

• Limit swimming if you suspect a chemical imbalance

• Use a cover to reduce evaporation and chemical loss

• Adjust filtration times to reduce strain on equipment

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Conclusion

If you’re topping up your pool more than usual, don’t ignore it. Pool leaks waste water, increase chemical use, and can lead to bigger problems if left unchecked.

Use the bucket test to confirm it’s not just evaporation, and follow this checklist to track down the source. Need sealants, O-rings or repair tools? Visit our pool products section for everything you need to fix small leaks fast — or get ready for professional help.

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Frequently Asked Questions