How to detect a hole in a basin?

Your pond water can evaporate during very sunny weather. During such times, your water loss may even reach 2 cm per day. At this level, it is not a problem.

But when you start to notice a significant and abnormal drop in the amount of water, it means there is inevitably a leak somewhere in your pond.

It could be a plumbing problem, but most of the time, a hole in your water feature is the cause. However, it is still not always easy to locate the leak in your pond. Since the goal is to solve the problem related to the watertightness of your setup, here are a few tips to help you locate the hole and patch it.

Where can the holes in your pond come from?

There are several reasons for holes appearing in your pond. First, if your pond is old, it may no longer be in good condition, especially if it was not designed with the appropriate equipment. If its liner is not made from the best materials, it may not withstand the test of time. In this case, regardless of the type of pond, it will eventually become defective and remain quite sensitive, especially in sunny weather, which can lead to leaks. But this wear and tear problem particularly affects ponds with PVC liners. They do not have a long lifespan and are therefore more exposed.

The leak in your pond could be caused by a hole in your liner from sharp objects that fell into the water at some point. This could be a rake, a pitchfork, etc. The leak could also be caused by rubbing against a tree branch. Still talking about sharp objects, this could also refer to aggressive plants whose roots or sharp rhizomes can really damage your equipment.

Even some fish can cause holes in the liner. This is the case, for example, with the diamond sturgeon, which has a body with many bony plates.

And as it grows, these plates also develop and become quite sharp. When moving in the water, they tend to rub against the walls, the bottom, and along the liner, which can quickly damage the equipment. When the pond liner is not made of concrete, it is more sensitive to this fairly common type of damage.

Leak or evaporation: the bucket test

Before emptying anything, make sure the drop is truly abnormal. In hot, dry, and windy weather, a waterfall or water jet significantly increases evaporation. The bucket test allows you to compare, under the same conditions, the pond water and water that cannot leak.

1. Place a bucket filled with pond water on a submerged step or next to the pond, in the same sun.
2. Mark both levels at the same time: a line inside the bucket, a marker (tape, stake) on the edge of the pond.
3. Leave it for 24 to 48 hours without topping it up and without rain if possible.
4. Compare: if the pond has lost significantly more than the bucket, there is a leak. If the two drops are similar, it is mostly evaporation.

Liner or water circuit: where to look first?

Many leaks do not come from the liner itself but from the circuit: pipe fittings, an overflowing filter outlet, or a waterfall where water passes behind a stone and escapes the liner. The easiest thing to do is to turn off the pump for a few days.

If the level stabilizes with the pump turned off, inspect the waterfall first: a stone that diverts the stream of water beyond the liner is enough to empty a pond in a few days. Our guide to building a stone waterfall on a liner shows how to build up the edges and direct the flow. Also check that the edge of the liner is not sagging under the soil or gravel: through capillary action, water can escape without there being a hole.

The different problems related to the presence of a hole in your pond
When you have a leak in your pond, it becomes a series of problems. The first, and most obvious, is that the water level drops rapidly in your aquatic environment. And at some point, it affects the flora and fauna of the setup. Especially during a period of high temperatures, a heatwave can quickly impact your plants and animals if they do not receive an adequate amount of water.

Even though some plants are capable of developing resistance to survive, in the event of a water shortage, fish are less resilient. They will therefore weaken after a while, and you can expect the worst if no solution is found to detect the leak and fix the problem. And even the most robust plants will eventually be affected, and your pond will be permanently destroyed.

How to locate a hole in your pond?

Detecting a hole in the pond is certainly difficult, but not impossible. To succeed, you must first temporarily turn off your pump. Then, you must let the water evaporate down to the level where you no longer notice a drop, and mark this area with a dot. Refill your pond to 10 cm above this area, and make sure the water stops at this same level to confirm that the leak is at this exact point. Pump the water, but make sure this time it is 10 cm below the marking point.

This step allows you to locate the leak area, and once that is done, all that remains is to find the exact location within this 10 cm radius. To detect the hole, check the area of the liner where the color is darker and the moisture is more pronounced. This color is generally black, and will be especially visible on an EPDM liner whose dry areas are grayish. The dark spot is the leak area. Now that you have detected it, all that remains is to find solutions to repair it.

How to patch a hole in a pond?

Once the hardest part is over, you will find it much easier to repair the hole. Regardless of whether your pond liner is concrete, PVC, or EPDM, there are repair techniques for each.

• Repairing a concrete liner: choose a time of day, and completely empty the pond. Then, thoroughly clean it with a brush before proceeding with the repair. Once your pond is clean, use a chisel and a mallet and cut a V into the hole. After this step, use clean water to clean the enlarged hole and remove all dust.

In a trough, mix 1/3 sand with 2/3 cement. Mix until you obtain a medium-thick, non-runny paste. Use it to completely fill the hole, then smooth it. Finally, cover it with a mesh, add another layer of your mixture, and smooth it. Wait for this area to dry completely before refilling with water.

• Repairing a PVC liner: empty the pond, clean your liner without using soap or other detergent products that could impact the balance of your pond's ecosystem, and use a liner patch that you will glue to the hole with a PVC-compatible adhesive.

• Patching an EPDM liner: the EPDM liner must also be cleaned before you repair the leak. Made from a rubber membrane, the EPDM liner is repaired with an EPDM patch and a suitable primer or adhesive. Choose a repair kit suitable for the hole, and make sure to degrease the area. Apply the patch and place the EPDM kit.

The presence of a hole in a pond is sometimes inevitable. The main thing is to notice it quickly and detect it, so that you can remedy it as soon as possible.

Preventing new holes

A well-installed liner lasts a long time. Most punctures come from what is underneath, what grows around it, or what falls into it. A few precautions greatly reduce the risk:

• Always place a geotextile felt between the ground and the liner: it protects against rocks, roots, and rodents.
• Remove stones and roots from the bottom of the excavation, and add a layer of sand if the soil is rocky.
• Avoid placing plants with piercing rhizomes or roots (bamboo, very vigorous reeds) nearby, or plant them in pots.
• Place large border or waterfall stones on a piece of additional felt, never directly on the liner.
• Do not leave sharp tools by the water's edge, and cut branches that rub against the liner outside the water.
• Monitor the level every week in summer: a leak detected early is easier to repair.

If you need to replace a liner that is too damaged, compare the materials in our selection of EPDM and PVC liners, and follow the installation steps in our guide building your garden pond with a liner. Adhesives, primers, and tapes are grouped in our adhesives and accessories for EPDM section.

Frequently asked questions