How to Find A Pond Leak
While some water loss in a water garden is normal due to evaporation and sometimes splash out, significant loss can be a problem and certainly frustrating. The first, and usually most difficult, step in fixing a leak in a pond is to actually find the leak. Follow these steps to make the job of finding a pond leak a little more efficient. The vast majority of pond leaks are not a hole in the liner. Step A helps you figure this out.
Step A in Finding a Pond Leak
Turn off the pump for a long enough period to be able to notice if the water is dropping at the same rate. We’d highly recommend using an air pump in the pond at this time to supply needed oxygen.
If the water level continues to drop, skip to Step C to continue the search for your pond leak. If the water level stays the same see Step B.
Step B in Finding a Pond Leak
You have now determined that the leak is not in the main pond. Now you need to narrow it down a bit further. The pond leak is either in the plumbing or in the waterfall / stream. Closely inspect your plumbing, particularly at any joints, make sure there is no leakage here. Depending on what equipment is installed on your pond you may be able to make further determinations if needed. For example, if you use a waterfall box that has the inlet at the bottom, you can put a plug in the inlet to see if the box holds water or might be the source of the leak.
Next, inspect your waterfall and stream for leaks. Most of the time, the problem is caused by plant matter or other obstructions raising the water level behind the weir and causing an overflow over the liner edge. Perhaps a stone has settled or your pond liner has slipped below water level in an area. If it hasn't rained in a few days, check around the perimeter for a wet spot. If you find one, you have a good idea of where to look closer for the source of the leak.
Check streambed edges for plants outside the lined area whose roots may have spread into the stream and vice versa for plants in the stream that may have ventured out. These plants can draw a significant amount of water out of the stream.
If you have a long stream bed you can narrow down the problem area by running your pump directly into the stream bypassing the top waterfall. Start a few feet up from the pond. Pump the pond water into this area and leave it running for 24 hours (or long enough to observe if the water loss is occurring). Then move the pipe return upstream 5-10 feet and repeat until the water loss occurs. This will narrow down the area that needs closer inspection.
If you still have not found the problem use the ideas in Step C in the streambed.
Step C in Finding a Pond Leak
At this point, you have determined that the leak is in the pond itself. Leave the pump off and allow the pond to continue to leak until it stops. If it does not stop before reaching a level dangerous to fish and plants, you will need to temporarily remove them from the pond. While the water level is dropping check around the edges to make sure that the pond liner has not sunken down or rocks have not been displaced. When the water reaches the point where it is no longer dropping it will be necessary to closely inspect the liner all along this water level to find the source of your pond's leak. You should be looking for any irregularity in the pond liner from a large gash or a tiny pinprick. For fast leaks you can try putting some milk in a squirt bottle and spraying into the water at the edges of the pond. The milk will cloud the water where there is no hole. It will flow toward the hole, if there is one. This method will not work for slow leaks.
Once you have found the source of your pond leak it is time to make repairs. If it was just a displaced liner, move everything back into place. If a hole was found in the pond liner, you can patch it following our Splicing and Patching Instructions.
Another often unseen cause of water loss
There are always other possible explanations for water loss in a pond. One that is often overlooked is displacement loss due to excessive groundwater. This is more common if the pond was installed in a low lying area of the yard and/or after very heavy rains. What happens is that the pressure from the groundwater pushes the liner up above the pond bottom. This forces the pond water to overflow the pond edge. When the groundwater recedes and the liner settles back in there is less water in the pond giving the impression of a leak.