Quick Answer
Is Water Loss in a Pool Normal, and When Does It Mean There's a Leak?
In outdoor pools, an average water level drop of 3–6 mm per day (roughly 1–2 cm per week) from evaporation is normal. If the drop is significantly higher than this, especially when it continues even with the pump off, a leak in the shell or piping should be investigated.
Normal Daily Evaporation
3 – 6 mm
Evaporation or Leak? A Simple Test
The 'bucket test' can help distinguish the two: place a water-filled bucket on the pool step, partially submerged, and compare the level drop inside the bucket versus the pool after 24 hours. If the pool's drop is noticeably greater than the bucket's, a leak is likely.
Leaks typically occur at pipe connections, skimmer/light gaskets, or shell cracks, and can be pinpointed with professional leak-detection equipment.