Pool Losing Water

Why Is My Pool Losing Water?

A dropping pool water level is one of the most common concerns Auckland pool owners raise. The good news is that not every drop in water level means a leak. The less good news is that a real leak, left unattended, can cause serious damage to your pool structure, equipment, and the surrounding ground.

This guide covers the two main causes of water loss, how to tell them apart, and when it's time to call a professional.

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Evaporation vs a Leak: What's the Difference?

Both evaporation and leaks cause your water level to fall, but they behave differently and have very different consequences.

Evaporation is a normal, ongoing process. Heat, wind, low humidity, and direct sunlight all pull water from the surface. In Auckland's warm summers, evaporation can be noticeable, particularly in pools without a cover.

A leak means water is escaping through a crack, a failed fitting, a loose connection, or damaged equipment. Unlike evaporation, a leak doesn't slow down when the weather cools. It continues regardless of conditions.

Signs it's probably evaporation

• Water loss is consistent and gradual
• Loss is higher during hot, windy, or sunny periods
• The pool has no cover, or the cover is rarely used
• No wet patches around the pool equipment or surrounding ground

Signs it could be a leak

• Water loss continues at the same rate regardless of weather
• You notice wet or soft ground near the pool shell, equipment pad, or return lines
• The pool loses more water when the pump is running than when it's off (or vice versa)
• You're topping up the pool far more frequently than usual
• There are visible cracks in the shell, fittings, or around fittings

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The Bucket Test: A Simple Way to Check

The bucket test is a straightforward method for separating evaporation from a leak. You don't need any special equipment.

What you'll need

• A standard bucket (around 10-15 litres)
• A marker or piece of tape
• 24-48 hours

How to do it

1. Fill the bucket with pool water and place it on a pool step or ledge so it sits at the same level as the pool surface. The bucket must be in the pool, not beside it, so both water bodies experience the same temperature and sun exposure.
2. Mark the water level inside the bucket with tape or a marker.
3. Mark the pool water level on the wall or skimmer box at the same time.
4. Leave the pump running on its normal cycle. Do not add water to the pool during the test.
5. After 24-48 hours, compare the two levels.

Reading the result

• Both levels dropped by the same amount: The loss is likely evaporation. No leak is indicated.
• The pool dropped more than the bucket: The difference points to a leak. The bigger the gap, the more significant the leak may be.

Run the test twice if you want to be confident, once with the pump running and once with it switched off. If the pool loses more water with the pump running, the leak is likely in the circulation system (pipes, fittings, or equipment). If it loses more with the pump off, the leak may be in the shell itself.

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Common Sources of Pool Leaks

Leaks can occur in several places. Knowing where to look helps you describe the problem clearly when you contact a professional.

The pool shell

Cracks in the plaster, fibreglass, or concrete shell are a common source of leaks, particularly in older pools. Small surface cracks don't always leak, but cracks that go through the shell will. Look for discolouration, staining, or visible gaps in the surface.

Fittings and penetrations

Skimmer boxes, return jets, main drains, and light fittings all penetrate the pool shell. The seals around these fittings can deteriorate over time. Check for movement, cracking, or water staining around each fitting.

Plumbing and pipework

Underground pipes can crack due to ground movement, tree root intrusion, or age. Leaks in buried pipework are harder to locate without pressure testing.

Equipment connections

Pump lids, filter tank o-rings, chlorinator unions, and valve fittings can all develop slow leaks. These are often visible as drips or wet patches around the equipment pad.

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What to Do If You Suspect a Leak

1. Run the bucket test to confirm water loss is above normal evaporation.
2. Inspect visible fittings and equipment for obvious drips, cracks, or wet patches.
3. Check the ground around the pool for soft, wet, or sunken areas that might indicate underground pipe leaks.
4. Note whether loss is greater with the pump on or off, this helps narrow down the location.
5. Contact a pool professional for a leak detection assessment. Locating leaks in buried pipework or the shell typically requires pressure testing and specialist equipment.

Do not delay getting a leak investigated. Even a slow leak can erode the ground beneath a pool shell, cause structural movement, and damage surrounding landscaping or structures over time.

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How Much Water Loss Is Normal?

Evaporation rates vary depending on weather, wind exposure, and whether the pool has a cover. As a general guide, some water loss on warm, windy days is expected. A pool with no cover will lose more than a covered pool.

If you are topping up your pool significantly more than once a week during normal conditions, or if the level is visibly dropping overnight, it is worth investigating further rather than assuming it is evaporation.

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Reducing Evaporation

If the bucket test confirms your water loss is evaporation rather than a leak, there are practical steps to reduce it.

• Use a pool cover when the pool is not in use. A well-fitted cover is the single most effective way to reduce evaporation.
• Reduce water features and fountains during hot or windy periods, moving water evaporates faster.
• Plant windbreaks around the pool area if wind exposure is significant, though this is a longer-term measure.

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When to Call a Professional

Contact a pool professional if:

• The bucket test shows the pool is losing more water than the bucket
• You can see cracks in the shell or around fittings
• There are wet or soft patches around the pool or equipment
• You cannot identify the source of the leak yourself
• The pool requires frequent topping up with no clear explanation

Leak detection and repair is not a DIY task once the source is unclear. Pressure testing buried pipework, repairing shell cracks, and resealing fittings all require the right equipment and experience to do properly.

Sparkling Pools has been servicing Auckland pools since 1992. If you suspect your pool has a leak, get in touch for an assessment.