Once you’ve taken a shot at identifying the type of liner you’re working with, it’s time to try to identify the type, location, and cause of the leak, if possible. When you notice that your pond has less water today than it had yesterday, you can be forgiven for assuming the problem is a hole at the bottom of your pond, somewhat like the drain at the bottom of your bathtub. But to be honest, that’s the least likely situation.
External Water Loss: Evaporation
Evaporation is the number one culprit in water loss, not leaks, particularly in the summertime. Warm weather, exposure to direct sun, and ponds with large surface areas increase the amount of daily water loss you’ll see. You can estimate the likely water loss by contacting your state’s water resources department or even a local university. Using the dimensions of your pond, they should be able to calculate your evaporative water loss in gallons per day.
Aside from perforations and tears in your liner from animal predation, weakness due to age or erosion, or simple liner shifts, water can also escape through leaks in your pond equipment. Since that’s the next easiest thing to check, let’s start there.
External Water Loss: Features
If you’ve got a stream or waterfall with your pond, the piping, pumps, and edging present even more opportunities for leaks, so your first line of defense is to scrutinize the edges of those features. As dirt and stones around the boundaries shift with the help of rain or curious creatures, low spots can form that allow water to escape over the edge of the liner. You’re likely to notice patches of wet mulch or squishy grass near the leak, which can help you zone in on the culprit. Fortunately, that’s the simplest type of leak to fix - just adjust the liner and lock it in place with a good-sized stone.
Splash leaks are also an easy source of water loss. Check out that gorgeous new shale boulder or carefully stacked slate tower. Is it catching water from your pond fountain and deflecting it out into the flowerbed? That may not look like a significant loss at first glance, but hours and days can add up, and so can the gallons. Again, this is a lucky problem to have - you can turn your boulder slightly or adjust the angle of the fountain, so any spray stays within the boundaries of the pond.
External Water Loss: Pond Equipment
Pumps, pipes, filters, automatic pond skimmers -- these are possible culprits for water loss in an otherwise tight ship. You can start by checking for standing water nearby, where the ground should typically be dry. If you find a wet spot, turn off or remove the equipment from your system for repair or replacement. Alternatively, you can eliminate this possibility by filling your pond all the way and turning off all the equipment. (Don’t do this too long, especially in warm weather — you don’t want to stress your fish.) Keep an eye on the water level. If it remains steady over a period where you’d expect to see movement, then you know the problem isn’t in the pond itself. In these cases, you’ll need to take another close look at the equipment.
Internal Water Loss: Installation Problems
Specific damage is one of the more challenging issues and may involve punctures and tears from external factors. During installation, holes and tears can come from rough handling, excessive stretching, punctures from protruding tree roots or sharp rocks, and even careless placement of tools or walking on the liner itself. Seams are also particularly vulnerable to leaks, and whether they’re taped (PVC) or glued (EPDM), tiny imperfections in seams made during installation are frequently your culprit. You might notice the effects of moderate seam leaks soon after filling your pond, but minor leaks may continue undetected for months and even years. After such a length of time, those tiny leaks have probably grown and triggered even more severe problems like erosion and instability in the soil nearby.
Internal Water Loss: Liner Damage
If a leak first appears some months or years after installation, you’ll need to consider a broader range of potential causes. To list a few examples, evident damage after installation can come from foot traffic, wildlife, or rocks and tree roots. Even if you carefully prepared your excavation, removed rocks, and cut tree roots, those can reappear some seasons later. Nearby trees continue to grow and reach your pond if excess moisture is present outside the liner. In a dry climate, something like innocently watering the plants placed around your pond’s edge could lead to a big problem. Likewise, especially if you have rocky soil, even a soft, lovingly raked surface may eventually sprout sharp stones as they work their way up through the layers. The relentless weight of water pressing down on an invisible sharp stone over time can tear or puncture your liner.
Storms can cause a lot of damage, even to a low-profile hole in the ground. Branches, twigs, lawn furniture - lots of things can end up in your backyard pond and leave rips and cuts as you wrestle them out.
Wildlife can damage your liner, too. If the liner is covered with only a thin layer of soil or other protective material, the sharp claws of cats and raccoons are just so many puncturing needles. Deer, dogs, and other larger animals have substantial weight and, having wandered into the pond unaware, may struggle to escape, shredding your liner in the process. Herons and other birds have razor-sharp beaks, and they love to make your fish-filled pond a regular hunting ground.
Internal Water Loss: UV Degradation and Age
UV exposure is a common bugaboo for artificially lined ponds. Plastic rigid liners, flexible PVC, and (to a lesser extent) EPDM liners all degrade after exposure to UV radiation in sunlight. Surprisingly, UV radiation can even penetrate shallow soil and clear water to over 100’. To be sure, the intensity of the radiation lessens the deeper it goes, but given years of mild exposure, even a vulnerable pond liner under 4 feet of water can weaken and degrade. Degraded liners become brittle and may crumble at the slightest touch or movement. Such badly decayed material is not repairable — this kind of damage requires complete replacement. Old liners may also exhibit similar degradation, even when it’s not clear that sunlight is the problem. Crumbling and extremely fragile liner material is a clear indication that it’s time for a complete replacement.