There are five common types of pond leaks:
Keep in Mind!
Evaporation occurs naturally with any body of water and can account for minor water loss. If there is high winds water loss can also occur-just be sure to shut off the waterfall if the wind is dispersing the water from the pond or water feature
Find the leak
Ensure your pond is full
Turn off all pumps and filtration
(keep aeration running if there are fish present in the pond)
Water level remains at the same level
You have determined that the leak is either water being diverted from the falls/stream or a leak from the hosing. Check along the hosing for any pin holes or cracks. Turn off your pond for a day or two then turn on and search for any wet areas along the hosing or near the falls to find the origin of the leak. A damaged hose can be cut and repaired using a coupling. A leak from the falls will usually require some shifting of rocks to redirect the water.
Option B: Edge of the Liner has Receded or Dropped
Often if the edge of the liner has receded or dropped there will be a patch of moist soil or aggregate where this has occurred. This is usually a tricky leak to find as there are often larger rocks or boulders that need to be removed from the edge of the pond to see the edge of the liner. Once you have found the leaking area, the liner can be lifted/repositioned and backfilled to prevent the liner from slipping back. As well ensure edge rocks are not shifting over time and repositioning the liner to cause a leak.
Option C: Crack or Leak from the Skimmer
Drop the water level below the skimmer. If there is a crack in the skimmer box it will likely have to be replaced. Usually the leak will be where the skimmer plate has been attached. This plate may have to be removed and resealed if this is the case. Ensure there is excess liner below the skimmer plate to keep the liner from stretching and tearing over time. Use a lap sealant to seal as it adheres to EPDM liner better than silicone. Also use lap sealant in the screw holes for a better seal.