Trouble Shooting Water LossAll backyard ponds will lose water from natural causes. Evaporation, or water vaporizing into the air, and consumption by animals and plants are some of the most common. Obviously, the water is naturally replenished through precipitation, though the rate of natural loss often is greater than the amount falling from the sky. Generally speaking this occurs during the hot summer months when evaporation is greater and rainfall amounts are less.
Some ponds are equipped with an "auto-fill" system that works to maintain the water level by automatically replenishing the lost water via a piped water source. These work great to "offset" the naturally lost water. Their negative is that they make any water loss unapparent and leaks may go unnoticed. Since most pond owners are without "auto-fills" they will notice a decrease in the pond's water level periodically. Naturally pond owners may ponder the question..."Do I have a leak?"
The first thing to consider is what is the "normal" rate of evaporation? This is difficult to answer since so many factors will affect this. These factors include: geographic location; exposure to sun, wind, shade, etc; method of re-circulation, i.e., a waterfall or fountain; and pond size and depth. Experience has shown that most ponds in the mid-Atlantic region will lose 1" to 2" of water in the course of a normal summer week. This can and will vary greatly dependent on listed factors, though generally speaking losses greater than this should be carefully scrutinized. New pond owners should be diligent in their observations of water levels in the pond and attempt to determine their specific rate of normal evaporation. Then it will be easier to tell if water loss is greater than normal, signifying a possible leak.
So let's assume after careful consideration of the above information that you feel the pond is leaking. There are two primary areas for leaks in backyard ponds, either the pond liner itself has a hole or other damage or water is escaping while it is being recirculated outside of the main body of pond water. Examples are, (though not limited to), waterfalls, out of pond filters/ pumps, or anywhere water is exiting the pond. Even a fountain or small "spitting" statuary can create water loss from wind or inadvertent splashing. Any and every point of connection in piping has the potential for leaking, and even the tiniest of drips will add up quickly, creating the loss of several inches of pond water overnight. So step one in leak investigating is to shut down all water flow outside of the pond and monitor water loss in comparison to the rate of loss while the water was recirculating. The water may be allowed to recirculate within the pond, i.e.; with the pump disconnected from the exit piping or air pump w/ air stone bubbler, during this period of observation if needed. Experience shows that greater than 90% of the time the water loss rate will appear to be less with the recirculating water off.
If the rate of water loss is less with the recirculating water off then follow the steps in Option A. If the water level continues to drop at or near the same rate with all out-of-pond re-circulation shut off this indicates the potential for a leak in the pond liner and you should proceed to Option B.
Option A: Now you can look for the leak source between the exit point in the piping to the return point back into the pond. Look carefully for wet/ damp spots around identifiable areas. Follow/ observe piping thoroughly. Once found the source of loss should be corrected. Disconnect/ reconnect and fittings/ connections in piping. Make certain any clamps are set squarely and tightened properly. Be sure any threads are wrapped in "plumbers" Teflon tape. Re-glue any joints as needed or contact a contractor to help. Recheck any repairs after a few days for water tightness. If the source of water loss is determined to be from flowing water within the stream/ waterfall, the easiest thing to do is to manipulate vertically the outer edge of the liner to "contain" the flowing water and keep it on the liner to completely return to the pond. The use of black, expanding foam (the type used for waterfall construction) is another option. Sprayed into gaps of dry rockwork the foam creates a fairly reliable seal (once cured) to at least divert water. Sometimes "homemade" waterfalls are created without any liner or any type of waterproofing under them. Unfortunately waterfalls of this type are likely destined to lose water until completely dismantled and rebuilt properly.
Certainly troubleshooting, finding and fixing leaks in backyard ponds can be tricky. Hopefully the above information will help the process.
Remember that ponds built professionally should be totally "backed-up" by the builder. A good contractor should be extremely helpful in these situations, so always contact them first if possible.