Troubleshooting 101: How to Find a Leak in a Pond Liner 

30/05/2023

Maintaining a pond can be a relaxing and calming experience for anyone fortunate enough to have one in their garden. However, as with most things, maintaining a pond can come with its issues, and sometimes one of those issues is finding a leak in a pond liner. A pond leak can be frustrating and time-consuming to troubleshoot, but with a few tools and methods, it can be fixed, and your peaceful oasis can be restored.

Establish the cause of water loss

It is natural to assume the worst when it comes to water loss in a pond, but you need to rule out other causes:-

Check for evaporation through sun temperature and wind: 

During hot or windy spells, it isn’t unusual to lose as much as 1 – 3 inches of water per week (depending on the size and depth of the pond).  Use a chinagraph pencil to mark the water level on the pond liner, or measure from a fixed point such as a slab to the water line and monitor the pond level daily for one week. 

The bucket test is a great way to identify if a pond is losing more water due to evaporation or leaks. 

1. Fill the pond to normal water level. Fill a 5-gallon bucket with pond water to about two-thirds from the top.
2. Place the bucket on the first or second step of the pond. Ensure the bucket is immersed in the pond by at least five inches.
3. Mark the water level inside the bucket.
4. Shut off the pump and autofill (if you have one), and mark the pond water level on the outside of the bucket.
5. Resume normal pond pump operation.
6. After 24 hours, compare the two water levels. If the pond water level goes down more than the bucket's water level, there is probably a leak. If levels are the same, only evaporation has occurred.

The first thing to check in the case of a pond leak is the water level. If the pond has lost a significant amount of water, that means there’s a bigger issue than evaporation. If the leak is small, the pond will lose an inch or three every week. A loss of more than 1-3 inches every day could suggest a large, unmissable leak. If the pond's surface is evaporating, you can check the water level by placing a marking on the skimmer faceplate or on the wall of the pond at the water level and checking it every couple of days.

Examine the perimeter of the pond for damage: 

Damaged pond liners can cause leaks, so it's essential to inspect the pond perimeter for any sign of mechanical damage to the liner. Animals, such as birds, foxes and dogs, can cause harm to the liner by puncturing or scraping it with their claws. It is also advisable to inspect the plants around the pond to determine whether their roots could have punctured the liner (Bamboo, in particular, can cause damage to pond liners). 

Check the pond liner levels: 

If the pond liner is fixed at variable levels this would mean that you could lose water out of an end or side where the liner is fixed lower down.  If possible, dig a shallow hole on the outside of the pond around the periphery to check whether the ground is wet.  If you find wet ground it could indicate that the pond levels are uneven, resulting in water runoff where the wet ground is located.

Check for capillary action water loss: 

It is sometimes possible that leaks to ponds are caused by the capillary/siphoning action of an absorbent material which is in contact with the water.  If, for example, you have decided to build a natural-looking pond and placed a geotextile or cloth on top of the pond liner before backfilling with earth or stone, it is possible that the water is being drawn up the sides of the pond into the anchor trench (digging sample holes outside the pond may help to identify whether this is occurring).  This can be avoided by encapsulating the protection layer by oversizing the pond liner and folding it back over the top of the liner (details can be found on this page, How To Build A Garden Pond - A Step-by-step guide, or, by cutting the protection layer around the periphery and covering both edges with stone to create a ‘capillary break’.

Turn off pumps and waterfall: 

If the above methods do not help locate a leak, the next step is to turn off any pumps or waterfalls that are in your pond. Wait for several hours, and then observe the water level once again. If the water level remains the same, it's likely that the leak is in your plumbing system. However, if the water level has decreased, this may indicate a leak in your pond liner.

Check for Evidence of a Leak: 

Lastly, Double-check the pond's perimeter for evidence of a leak and check the waterfall boxes, pumps, and water return lines. A small leak can easily cause a big issue if not resolved immediately. Once you have identified the leak, patching it up can be quite an easy process. Remove any debris or external materials surrounding the leak and allow it to dry. Clean the area with a mild solvent taking extreme care not to release harmful solvents into the pond, as this would cause harm to your fish stock or wildlife.  Apply the approved pond liner sealant or pond liner patch material to the affected area and let it dry for some hours.

Conclusion: 

Finding a leak in a pond liner can be a daunting task but is manageable with some basic checks and tests.  Performing regular maintenance checks can help identify any issues that could cause pond leaks, such as sharp edges and debris that can puncture the liner. By performing the above steps, the source of the problem can be identified and rectified, and your tranquil pond can be restored.

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