Why Is My Pond Losing Water?

A pond dropping an inch or two of water sends most owners straight to the worst-case fear, a hole in the liner, and straight to the worst first move, draining the pond to hunt for it. Hold off. The great majority of pond "leaks" are not punctures at all. They are normal evaporation mistaken for a leak, water splashing out of a waterfall, or water quietly wicking and running out at the edges of a stream or waterfall, and every one of those is found and fixed without draining anything. A true liner puncture is real but uncommon, and even then you locate it with a simple test rather than by emptying the pond and searching blind.

The whole job is to narrow down where the water is going, from the easy and common to the rare and hard, before you touch a repair kit. This guide walks the diagnosis in order: rule out evaporation with a bucket, use the pump-off test to separate a waterfall or plumbing leak from a basin leak, use the pond's own level to pinpoint where a basin leak sits, and then work the short list of usual suspects. Do it in that order and you will almost always find the water without ever draining the pond.

First, is it just evaporation?

Evaporation is the number one false alarm, so rule it out before anything else. In warm weather a pond normally loses roughly an inch a week to evaporation, and more, up to an inch a day, when a large waterfall or stream is running in hot, dry, windy conditions, because all that moving, airborne water evaporates fast. One experienced keeper puts the baseline plainly: "It's very common to lose an inch a day in most ponds in the summer. I would guess you could also lose at least that much with a long stream due to evaporation." If your loss is in that range and worst on hot, breezy days, it is very likely just evaporation, and topping off is all you need.

To be sure, do the bucket test. Fill a bucket with pond water and set it on the pond shelf or beside the pond so it sits in the same sun and wind, mark both the pond level and the bucket level, and check them after a day or two. If the pond and the bucket drop about the same amount, you are watching evaporation, not a leak. If the pond drops noticeably faster than the bucket, the extra loss is a real leak, and the next tests will find it.

The pump-off test: waterfall or basin?

This is the single most useful test in pond leak-hunting, and it splits the problem in half. Turn off the waterfall and pump, top the pond back up to full, mark the level, and leave it off for several hours or overnight. Then read the level. The logic, as keepers repeat it, is simple: "Turn off pumps. if water drops you have a leak in the liner. If not then it's either the plumbing or waterfall." If the water holds steady with the pump off but drops when it runs, your leak is somewhere in the waterfall, the stream, or the plumbing, which is where the large majority of pond leaks live. If it keeps dropping even with everything off, the leak is in the basin itself.

When the test points at the waterfall, that is good news, because those leaks are the easiest to fix and never involve draining the pond. One keeper's result is the common one: "I have switched my waterfall and filter off and the water hasn't gone down! So I'm guessing the fault lies there's." From there you inspect the stream and the waterfall spillway, top to bottom, for where it is escaping.

The find-its-level test: pinpoint a basin leak

If the pump-off test says the leak is in the basin, do not drain the pond to search it. Let the pond do the work for you: leave the pump off and let the water drop on its own until it stops falling. Water only escapes down to the level of the leak, so wherever it stabilizes is the height of the hole or low spot, and now you have a narrow band to inspect instead of a whole liner. Run your eye and your hand around the pond exactly at that waterline, looking for a puncture, a settled edge, or a spot where the liner dips below the rim. This turns "somewhere in the pond" into "along this one line," which is the difference between a ten-minute find and a wasted afternoon.

The usual suspects, most to least common

Once the tests have pointed you at the waterfall or a waterline, the cause is almost always one of these, listed from most to least common:

• A low or settled edge, especially at the waterfall. The most common real leak of all. Over time an edge settles, or the liner was trimmed a hair low at one point, and water runs out there, worst where the waterfall meets the pond. As one keeper spotted from a photo, "the water is probably running under the lip of the waterfall edge and out where it sits on the pond edge." Check the whole rim, and the waterfall especially, for any point the water can crest.
• Wicking at the stream and edges. Underlayment fabric, and even rock and soil, act like a wick: if the fabric or a rock bridges from the water up over the liner edge, it draws water out by capillary action and drips it into the ground, silently, all day. Any fabric must be tucked below the water line, never left bridging over the rim.
• Splash-out. A waterfall hitting rocks at the wrong angle, or a stream that has shifted, can throw water outside the liner. It looks like a leak and is just aim.
• Skimmer and waterfall-box faceplates. Where a skimmer or a biofall box seals to the liner, the gasket and bolts can weep. A leak that tracks to one of these fittings is a re-seal, not a liner job.
• An actual hole in the liner. The rarest of the common causes, and the one everyone fears first. Usually a puncture from a sharp rock or root, found at the waterline by the level test.

How to fix what you find

Most of these fixes cost nothing. A low edge is raised: build the rim or the waterfall edge back up with soil or a shim of liner so the water can no longer crest it, and a keeper's shorthand for the waterfall version is to seal the fold with expanding foam and lift the edge, "a blast of waterfall foam in the fold. Or make sure the edge is higher then a few inches." Wicking is stopped by folding or trimming any fabric down below the water line so nothing bridges the edge. Splash-out is re-aimed by moving a rock. A weeping skimmer or waterfall-box faceplate is fixed by tightening the bolts evenly or replacing the gasket.

Only the actual liner hole needs a product, and it is a patch, not a new pond: an EPDM repair kit with a patch and seam tape or primer bonds over a clean, dry puncture and holds for years. Drain only to just below the hole, clean and dry the area, apply the patch per the kit, and refill. A whole re-line, laying a fresh EPDM liner in, is the last resort, reserved for a liner that is brittle, torn in many places, or a failing preformed shell that is cheaper to replace than to chase.

Pond water loss questions, answered

How much water loss is normal for a pond?

Roughly an inch a week in warm weather is normal evaporation, and a pond running a large waterfall or stream in hot, dry, windy conditions can lose up to an inch a day without any leak at all. Confirm it with the bucket test: set a bucket of water beside the pond in the same sun and wind and compare the drop over a day or two. If the pond and bucket fall about equally, it is evaporation; if the pond falls faster, you have a real leak to find.

How do I find a pond leak?

Work from easy to hard. Rule out evaporation with the bucket test. Then turn off the waterfall and pump, top up, and mark the level: if it holds with the pump off, the leak is in the waterfall or plumbing; if it keeps dropping, it is in the basin. For a basin leak, let the pond fall until it stops, the leak sits right at that waterline, so inspect that line for a settled edge, wicking fabric, or a puncture. You almost never need to drain the pond.

Why does my pond only lose water when the pump is on?

Because the leak is in the moving-water side, the waterfall, stream, or plumbing, not the basin. When the pump runs it pushes water up to the waterfall, where a low edge, a shifted rock, splash-out, or fabric wicking at the stream lets it escape; turn the pump off and the pond holds level because that path is no longer carrying water. Inspect the waterfall spillway and the stream edges top to bottom for where the water crests or wicks out.

Can I patch a pond liner leak?

Yes, if the leak really is a hole in the liner, which is the least common cause. An EPDM repair kit patches a puncture with a patch and seam tape or primer that bonds to a clean, dry surface and lasts for years. Drain only to just below the hole, clean and dry the spot, apply the patch per the kit, and refill, no full drain or re-line needed. Save a complete re-line for a liner that is brittle or torn in many places.