Have you ever thought about the almost insurmountable problems in making a pond waterproof? Is a completely waterproof pond an impossible dream? Substantial leaks need attention, no doubt about it. However, at some point or the other, insanity will overcome you, before each and every leak is found and fixed in the average pond.
The three primary sources of leaks are - waterfalls/streams, pipework, incorrect sealing. Waterfalls are a major culprit for leaks. Any splashing, no matter how minor, will result in water loss. Added to this is the reality that waterfalls or water courses develop hairline cracks between rocks and cement at some stage or the other. There is also natural evaporation to be taken into account as well.
But my pond goes down several centimetres each day - there must be a massive crack in the floor. How can tiny hairline cracks around pipe work or in the waterfall together with splashing loose substantial water from your pond you ask? Yes, definitely. If a single drop of water leaks out of your pond each second you will lose about 3.5 - 4 millilitres of water each minute. This is 240 ml per hour or 5,7 litres of water each and every day of the year. That's over 20,000 litres a year!
A 20,000 litre pond that is never topped up, will be completely emptied in ten months by an "insignificant" leak or splash of 10 drops of water each second, somewhere in the system. And this is not taking into account natural evaporation. Evaporation is higher in summer and high winds.
The effect of leaks on the pond will depend on the volume. Larger ponds may not show minor leaks but a pond of 12,000 or 15,000 litres will. A pond of this capacity can have a surface area of about 4 meters by 3 meters and a depth of a meter. Loosing 10 drops of water each second will lower the surface by about 3,5cm each week. Looked at in another way, every second week this pond will loose about 8 - 10% of it's water. All you have to do is top the pond up as a 10% water change is recommended each week. This may be better than driving yourself mad trying to find the leak.
However, it is always advisable to find the source of leaks. Once found, the problem is 80% cured.
Bottom drains are always a potential area for leaks. There are numerous pond builders who simply join 110 mm piping together beneath the pond floor using the standard rubber seal. This rubber seal is used when 110 mm piping is utilised for drains on buildings. These drains are not under any pressure what-so ever. However, on a Koi pond there is substantial pressure. The deeper the water the greater the pressure. The rubber seal may work initially but invariably leaks develop. All piping beneath the pond must be correctly glued and supported.
The piping that enters the pond shell as a bottom drain needs careful attention. Firstly the piping needs to be supported or built as part of the shell itself. This will prevent movement at some time or the other. Bottom drains and the floor of the pond are two completely different materials (plastic and concrete) in contact with one another. They have different properties with regard to flexibility. Hair line fractures can occur at the interface between the pipe and the concrete floor. Any movement of the soil beneath the shell, where the pipes are laid, will result in the pipe separating slightly from the concrete. Building the pipe work or the bottom drains into the shell will prevent movement.
Waterfalls will always be a source of leaks. Perhaps all waterfalls should be built on a sheet of plastic. Many headaches will be avoided. If a leak develops the water will flow back into the pond via the plastic sheeting. Interestingly a source of leaks on waterfalls is often under the stones. Hairline cracks develop between the stones and cement layer between them. These hair line cracks act as capillary tubes and literally suck the water out of the pond. It is capillary action, in the stem of trees, that provides massive amounts food and water to the leaves. If you suspect the waterfall is leaking I would suggest looking under the stones first, you will invariably find the leak.
Evaporation is also a major cause of water loss. The rate of evaporation is affected by factors such as the temperature of the air, the humidity of the atmosphere in the area, wind, and intensity of the sun. The evaporation is aggravated by splashing pond water over waterfalls, along streams and fountains to dissolve oxygen and dilute the impurities.
Before you drain the pond to reseal or concrete in the bottom drains, before your grind down the walls to re-plaster the pond look for the little places where small amounts of water can be escaping. Water leaks are relentless and combined they could very well be the source of substantial water loss. Fix them before you spend a great deal of money.
It is a time consuming art to find and fix leaks. I would suggest the pond owner try to do this himself. It would not be economical for pond builders to return every week to fix a series of minor leaks that could develop over time. Pratleys standard setting putty sets under water and should be in the repair kit of every pond owner. The putty can be used anywhere in the pond against cement and is especially convenient for repairing hairline cracks under stones. Pratleys will not adhere to rubberised and bitumen based sealers.
Bitumen sealers and rubberised paints are a problem when they leak. The moisture gets behind the coating and bubbling and leaking occurs. Unfortunately painting directly over the affected areas does not solve the problem. A leaking pond sealed with these types of sealers would have to be completely drained and the sealer completely removed by grinding down to the plaster to be successfully re- sealed.