Leak in a pond waterfall: how to detect it within 48 hours (and fix it for good)

When a customer calls us because their pond is “losing water,” our first question is always the same: do you have a waterfall or stream? In the vast majority of cases we see, the leak is not in the pond but in the waterfall system. It makes sense: this is where the water flows quickly, splashes, passes between stones and runs along liner edges that are rarely finished as carefully as those in the pond.

Test 1: pump off

Fill the pond to its normal level and mark it with a stake or a piece of adhesive tape on a stone. Turn off the pump for 24 to 48 hours, ideally without rain or extreme heat.

• The water level remains stable (to the nearest millimeter, allowing for evaporation): the pond is watertight, and the leak is in the circuit. Move on to test 2.
• The water level drops then stabilizes: the leak is in the pond, at the height where the water stops.

Think of the fish: with the pump off, keep the water aerated if it is warm.

Test 2: isolate the waterfall

Disconnect the pipe where it enters the waterfall and let it flow directly back into the pond. Turn the pump back on for 24 hours.

• Stable water level: the pump, pipe and filter are watertight. The leak is in the waterfall itself.
• Dropping water level: check the connections, the filter (cover, seal, overflow) or a leaking buried pipe.

Test 3: inspect the waterfall

With the waterfall running, walk around it slowly while observing and touching:

A tip for difficult cases: pour a few drops of food coloring or milk into the still water near a suspected area. If water is being drawn away, the cloud moves toward the leak.

The most common repair: raising an edge

Over time, the soil settles beneath the stones and the liner edge drops a few centimeters. All it takes is for this edge to fall below the surface of the flowing water for the waterfall to drain into the garden, sometimes at a rate of hundreds of liters per day. The correction is simple: lift the stones, raise the liner, slide firmly compacted soil behind it to hold it in place, then replace the stones. The liner edge must always extend clearly above the highest level the water can reach, including splashing.

Joints: the tile principle

When the waterfall has its own liner, it must overlap the pond liner like one roof tile overlaps the next: the upstream liner over the downstream liner, with a generous overlap. An overlap in the wrong direction allows water to seep between the two. On EPDM, the joint can be bonded with seaming tape applied over primer, on a clean, dry surface.

Seal beneath the spillway stones

A successful waterfall carries water over the stones, not underneath them. When most of the flow disappears beneath a stone, it runs between the stone and the liner and can reach an edge that has not been raised enough. A sealant compatible with aquatic life, applied beneath and around the stone, forces the water to flow over it.

Read also

If test 1 shows that the pond itself is leaking: How to find a water leak in a pond?.

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Frequently asked questions

— How much water does a waterfall normally lose?

A waterfall increases evaporation, especially in hot and windy weather, but this loss remains around a few centimeters per week. If you need to add water every day, there is a leak.

— The leak only appears after a few hours of operation. Why?

It is often debris (leaves, filamentous algae) that raises the water in an intermediate pool until it spills over an edge. Clean the spillways and check the edges in the catch basins.

— Can the hose connection at the top of the waterfall leak?

Yes, especially with barbed fittings without a clamp or with a loose clamp. If the leak is behind the waterfall, check this point first.

— Do I need to rebuild the entire waterfall?

Rarely. In the vast majority of cases, raising an edge, correcting an overlap, or sealing underneath a stone is enough.

In summary

• Pump switched off for 48 hours: water level stable, the leak is in the plumbing.
• Pump running without the waterfall: water level stable, the leak is in the waterfall.
• Look for damp soil, sunken edges, splashes, and wicking effects.
• Upstream liner over downstream liner, with edges always above the turbulence.

Last updated: September 28, 2026.