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—Leaks and diagnostics

When an automatic top-up hides a leak

An automatic top-up keeps the level steady, which is exactly why a leak can go unnoticed for months.

Auto-fill devices add water whenever the level falls below a set point. They are convenient, but they mask loss: the pool always looks full while water leaks away and is replaced. Clues include unusually high water bills, the top-up valve running frequently, damp areas around the pool, or chemical balance drifting due to constant fresh water.

Diagnostic guides describe what an owner can observe safely. They do not locate a fault; testing on site does that.

To check, the top-up is isolated and the level is marked and recorded daily, alongside a bucket test for evaporation. If the pool loses more than evaporation accounts for, there is a leak to trace. Once repaired, the top-up can be re-enabled with confidence.

01Summary

What matters most here

  • Top-ups mask loss

    The pool always looks full.

  • Watch the bills

    Rising water use is a clue.

  • Isolate to test

    Then measure loss.

02Detail

Signs of hidden loss

  • Water bills

    Higher than expected.

  • Frequent filling

    The valve running often.

  • Chemistry drift

    Fresh water changing the balance.

  • Damp areas

    Around the pool or plant.

03Before you start

How to check

  • Turn off the top-up

    At its isolation valve.

  • Mark the level daily

    For a week.

  • Run a bucket test

    To compare with evaporation.

—In practice

How to use this

Switch off the automatic top-up for a few days and measure how far the level falls. Check your water bills for unexplained increases, and notice how often the top-up valve runs. If the loss is more than evaporation would explain, start leak detection before the hidden loss causes damage around the pool.

Mistakes worth avoiding

Never checking the top-up
A top-up that runs frequently can hide a substantial leak for months, while water reaches the ground around the pool.
Ignoring chemical drift
Constant fresh water from a top-up changes water balance. Unexplained drift is a clue that water is being lost and replaced.

04FAQ

Common questions about this

Is it normal for the top-up to run?
Yes, to replace evaporation; frequent running beyond that is a clue.
How do I isolate the top-up?
Usually with a valve on its supply line.
Can a top-up valve itself leak?
Yes, it can overfill or leak; check it too.
Should I keep the top-up off?
Until loss is measured and any leak repaired.

05Read next

More pool guides on this

Filed under technical diagnostics & leak detection. Every pool guide is listed on the pool guides page.

—NEXT

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