Pond maintenance often involves the discovery of unexplained water loss. While some decrease in water level is expected due to natural processes like evaporation, a rapid or significant drop usually signals a structural problem. Successfully resolving the issue requires accurately diagnosing the cause and location of the water escaping the system. Understanding the difference between normal loss and a true leak is the first step toward effective repairs.
Identifying the Source of Water Loss
The first step in diagnosis is determining the actual rate of water loss, distinguishing it from normal evaporation. The “bucket test” provides a reliable measurement: place a container of pond water in the pond and mark the water level both inside and outside the bucket. After 24 to 48 hours, if the pond’s water level has dropped significantly more than the water level inside the control bucket, a leak is present. This comparison accounts for environmental factors affecting evaporation.
Before draining the pond, conduct a thorough visual inspection of the periphery, plumbing, and features. Look closely at the edges of the liner, around skimmers, filters, and pipe penetrations for wet soil or moist spots nearby. Many leaks are found within the first few feet of the pond edge where the liner meets the surrounding landscape or equipment.
If the leak is not immediately visible, allow the water level to drop naturally to help pinpoint the problem area. Mark the initial level and monitor the drop daily. When the water stops dropping, the leak is located at the new, stabilized water line, making a focused search easier. This process isolates the leak to a specific horizontal band around the pond perimeter.
Repair Methods for Lined Ponds
Leaks in lined ponds, whether flexible or rigid, require lowering the water level below the point of damage to ensure a dry working surface.
Flexible Liners
For flexible liners, such as EPDM or PVC, the repair area must first be meticulously cleaned to ensure proper adhesion. Specialized cleaning solvents or isopropyl alcohol should be used to remove any algae, dirt, or oils from the surface surrounding the hole. Once the area is dry and clean, a primer may be necessary for some patching materials to promote a strong chemical bond. Self-adhesive patch kits, often made of the same material as the liner, are then applied over the damaged section, extending several inches beyond the perimeter of the hole. For tears along seams, specialized seam tape or liquid liner sealant is applied to fuse the edges together.
Rigid Preformed Ponds
Rigid preformed ponds, typically made of fiberglass or high-density plastic, require a different approach to fix cracks. Because these materials expand and contract with temperature changes, the repair needs to be flexible yet strong. Small hairline cracks can sometimes be sealed with underwater-curing epoxies or specialized mastics designed for plastic or fiberglass structures. Larger cracks require structural reinforcement to prevent recurrence under hydrostatic pressure. This involves using a two-part epoxy kit, sometimes incorporating a fiberglass mesh layer for added tensile strength. Proper preparation involves sanding or roughing the surface to create a better mechanical bond for the sealant.
Sealing Natural and Earthen Ponds
Ponds built directly into porous soil, such as sand or gravel, often leak due to poor soil composition rather than a localized hole. The most common solution for these earthen bodies is the application of sodium bentonite clay, a natural material known for its capacity to swell significantly when wet. This swelling action fills the voids between soil particles, creating a low-permeability barrier.
Bentonite Application Methods
Bentonite can be applied using the “blanket method,” where a layer of the material is spread across the exposed pond basin. This layer is then covered with several inches of native soil to protect the bentonite from erosion once the pond is refilled. The weight of the water helps to compress the blanket, activating the sealing process.
Alternatively, the “mix method” involves tilling the powdered bentonite directly into the top six inches of the existing soil across the pond bottom. After mixing, the soil must be heavily compacted using heavy machinery. Proper compaction ensures the bentonite particles are pressed tightly against the soil structure, achieving high sealing effectiveness.
Polymer Sealants
For very large earthen ponds or reservoirs, specialized polymer sealants offer another option, often applied directly to the water surface. These polymers are designed to sink and seek out areas of high water flow, effectively plugging porous pathways in the soil. Unlike bentonite, which requires draining, some polymer products can be applied while the pond is full, allowing hydrostatic pressure to drive the material into the leak path.
Fixing Leaks at Edges and Structures
Many leaks occur at the periphery or around structural elements rather than in the main basin.
Capillary Action
Capillary action is a frequent culprit, where water wicks over the edge of the liner and into the surrounding dry soil. This happens when the liner edge is not sufficiently elevated above the final water line. Resolving this requires ensuring the liner edge, or a constructed berm just inside the edge, is always higher than the maximum pond level to break the capillary path.
Waterfalls and Stream Beds
Waterfalls and stream beds are common leak points due to the complexity of sealing the liner around natural rock formations. Water can easily find a path underneath or beside the liner if the material is not properly tucked and sealed against the rocks. Applying specialized waterfall foam, a non-toxic expanding sealant, is effective for filling small gaps between rocks and the liner. The foam cures quickly and permanently seals the interface between the liner and the decorative stonework, redirecting water flow back over the intended path.
Plumbing and Skimmers
Leaks around plumbing penetrations, skimmers, and filters often stem from compromised gaskets or seals. When a pipe passes through the liner, a watertight flange and gasket system is necessary to maintain integrity. Over time, these seals can degrade or shift, necessitating the replacement of the gasket or the application of a flexible, underwater-safe sealant around the exterior of the fitting. The connection between a skimmer faceplate and the liner must also be regularly checked for loose screws that may compromise the watertight seal.