Natural Pond Handbook

38 · Leak Detection & Liner Repair

A dropping water level is almost never "evaporation." Here is how to find and fix the leak without draining the whole pond.

Step 1 — locate the leak level

Stop top-ups and mark the water line. If it keeps dropping to a specific level and stops, the leak is at that line (side puncture, fitting, or behind the waterfall). If it drops below the liner rim and never stops, water is leaving via overflow or an edge.

Step 2 — the dye test

With the pump off and water still, squeeze a few drops of food colouring near suspect seams, folds, and fittings. The dye will be drawn into the leak. Check edges, liner folds behind waterfalls, and any penetrations first — those are the usual culprits.

Common leak points

  • Liner pulled down at the top edge (animals, frost heave).
  • Punctures under sharp rock or from a stray root.
  • Leaks at pipe penetrations and waterfall seams.
  • Plumbing fittings outside the liner (these are plumbing leaks, not liner leaks).

Repairing EPDM

  1. Dry and clean the area; roughen with a scuff pad.
  2. Apply EPDM primer, wait as directed.
  3. Bond a patch (or seam tape) with a roller; allow full cure before refilling.
Under-liner leaks If water seeps under the liner (failed sub-soil), you may need to lower the pond, add a French drain, or accept a slight perpetual top-up. A pro with leak-locating gear can pinpoint it.
Leak detection procedure
  1. Mark the water level with a pencil line on the pond edge.
  2. Turn off the pump and wait 24 hours.
  3. Check the mark: if the level dropped, the leak is in the liner or base. If it did not drop, the leak is in the plumbing or connections.
  4. Inspect visible liner for damage, punctures, or exposed areas.
  5. Use food colouring near suspected areas — watch where it appears.
  6. Repair with EPDM patch: clean area, apply primer, press patch firmly, hold for 60 seconds.
Patch repair tips
  • Patches work best underwater — the water pressure helps bond the adhesive.
  • Round patches are stronger than square ones (no corners to peel).
  • Overlap any existing patch by at least 50 mm.
  • If the leak is in a fold, add extra underlay behind the fold to prevent recurrence.