Find and Fix a Pond Leak
Losing water? Use the bucket test to tell a leak from evaporation, then check the waterfall, stream, and liner edges first before suspecting a puncture. Here is how to find and repair a pond leak step by step.
A pond that keeps dropping has two possible explanations: normal evaporation or an actual leak, and your very first job is to tell them apart with the bucket test. If it really is a leak, the good news is that most leaks are not mysterious holes in the bottom. They are almost always along the waterfall, the stream, or the edge of the liner where it has folded or settled below the waterline. Check those high-energy areas first, narrow down the waterline where the level stabilizes, and most leaks turn out to be a simple fix with an EPDM patch or a repositioned rock.
Liner Repair Supplies
Aquascape EPDM Liner Repair Patch (8.5 in)
$10.39 on Amazon
Brand-name self-adhesive patch made for ponds, streams, and water gardens.
ToLanbbt EPDM Liner Repair Patch Kit (8 x 8 in)
$9.97 on Amazon
Peel-and-stick waterproof patches for quick punctures and small seam fixes.
Sibosen Large EPDM Repair Patches (12 x 12 in, 5-pk)
$17.99 on Amazon
Bigger self-adhesive patches for larger tears or covering several spots.
Sibosen EPDM Repair Patches (8 x 8 in, 5-pk)
$12.99 on Amazon
Multipack of thickened self-stick EPDM patches to keep on hand for repairs.
Step 1: Is it a leak or just evaporation?
Before you tear anything apart, confirm you actually have a leak. Ponds lose water to evaporation every day, and in hot, dry, windy weather that can be an inch or more per week, more if you have a big waterfall or stream throwing water into the air.
The bucket test
This simple test settles it. Fill a bucket with pond water and set it on a step or shelf so its water level lines up with the pond's surface. Mark the water level on both the bucket and the pond. Run the pond normally for one to two days, then compare. If the pond has dropped noticeably more than the bucket, you have a leak. If both dropped about the same amount, you are just watching evaporation and there is nothing to fix.
Step 2: Narrow down where the leak is
Once you know it is a leak, let the pond tell you roughly where. The trick is to watch where the water level stops falling.
- Turn the pump off and watch. If the level keeps dropping with the pump off, the leak is somewhere in the main basin, below the line where it eventually stabilizes.
- If it only drops with the pump running, the leak is in the waterfall, the stream, or the plumbing, not the basin. This is the most common scenario.
- Note the stabilized waterline. Wherever the water settles and stops falling is exactly the height of the leak, so inspect the liner edge right at that line.
Step 3: Check the usual suspects first
Save yourself a lot of digging by inspecting the places leaks actually happen, in order.
The waterfall and stream
This is the number one culprit. Over time, settling soil, shifting rocks, or a build-up of debris can divert water so it runs out behind or beside the stream instead of back into the pond. Run the pump and watch the stream edges closely for water escaping over a low spot or wicking out behind the liner. Re-set any rocks that have slumped and make sure the liner edges along the stream sit well above the water flowing past them.
The liner edges and folds
Walk the entire perimeter and check that the liner is higher than the water all the way around. A single low corner, a fold that has settled, or an edge that has slipped down lets water wick out steadily, especially where capillary action pulls water into surrounding soil or a gravel bed. Lifting and re-supporting a sagging edge often stops the leak completely with no patching at all.
Punctures in the liner
If the waterline stabilized low in the basin, look for a puncture at that depth. Roots, sharp stones working up through the underlayment, or a dropped tool can pierce EPDM. Once the pond is down to the leak level, you can usually see or feel the hole as a damp patch or a visible nick.
Step 4: Repair the liner
EPDM liner is very repairable. For a clean, lasting patch:
- Drain to below the hole so the area can be worked dry, and if fish are present move them to safe, dechlorinated holding water if the level must drop a lot.
- Clean the area thoroughly. Scrub off algae, grease, and grit, then dry it completely. A patch will not bond to a slimy or wet surface.
- Cut a patch with rounded corners that overlaps the hole by several inches on every side. Rounded corners resist peeling.
- Press firmly. Apply the self-adhesive patch and roll or press out all air, working from the center outward for full contact.
- Let it cure per the product instructions before refilling, then top up with dechlorinated water.
For large tears, failed factory seams, or a liner that has gone brittle with age, a patch may not hold, and a professional repair or a liner replacement is the wiser call. If you do end up replacing the liner, size it correctly with our pond liner calculator so you have enough material and overlap.
Refill and protect water quality
Whether you patched a hole or just re-set an edge, refill with dechlorinated water. Big top-ups of untreated tap water add chlorine that harms koi and the beneficial bacteria in your filter, so always treat the water and confirm your true pond volume before dosing dechlorinator. Once the pond holds steady for a few days without dropping faster than the bucket, your repair is good. While the water level was disturbed, it is also worth a quick check of the nitrogen cycle to make sure your readings settle back to zero ammonia and nitrite.
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Frequently Asked Questions
How do I know if my pond is leaking or just evaporating?
Use the bucket test. Fill a bucket with pond water, set it on a shelf or step so the water level matches the pond, and mark both levels. After a day or two with the pump running normally, compare the drop. If the pond falls faster than the bucket, you have a leak. If both drop about equally, you are seeing normal evaporation, which can be an inch or more per week in hot, windy weather.
Where do most pond leaks happen?
The vast majority of leaks are not in the bottom of the pond but along the waterfall, stream, and the edges of the liner. Water escapes where the liner is folded low at a corner, where it has settled below the waterline, or where a stream has shifted and lets water run out behind the rocks. Always check the highest-energy areas, the waterfall and stream, before you suspect a puncture in the main basin.
How can I find exactly where my pond is leaking?
Let the pond drop on its own with the pump off and watch where the level stabilizes. If it stops falling at a certain point, the leak is right at that waterline, so inspect the liner edge there. If the level keeps dropping with the pump off, the leak is low in the basin. If it only drops with the pump running, the leak is in the waterfall, stream, or plumbing. This narrows the search fast.
Can I repair an EPDM pond liner myself?
Yes, small punctures and tears in EPDM liner are very repairable with a self-adhesive EPDM patch or a liner repair kit. Clean and dry the area thoroughly, round the patch corners, and press it firmly over the hole with several inches of overlap on all sides. The liner must be clean and free of algae and grease for the patch to bond. For large tears or failed seams, a professional liner repair is the safer route.
How much water loss is normal for a pond?
Normal evaporation varies with weather, but losing roughly 1 to 3 inches per week in hot, dry, windy conditions is common, and a pond with a large waterfall or stream loses more because of the increased surface area and splash. A healthy pond should not need more than the occasional top-up. If you are adding water every day or two to keep it full, that is a leak, not evaporation.
Should I keep topping up a leaking pond while I fix it?
You can, but always use dechlorinated water, because frequent large top-ups with untreated tap water add chlorine that harms fish and beneficial bacteria. Heavy topping up also dilutes your water chemistry and can stress koi. It is fine as a short-term measure while you locate and repair the leak, but treat it as a stopgap. The goal is to find and fix the leak, not to refill the pond indefinitely.
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