Frequently Asked Questions - Phantom water leaks from ponds

Natural style stream in Forest of Dean Sandstone by Peter MayCheck when the leakages occur. Is it when a fountain is in operation?

Is it only when the waterfall is in operation?

Is it only when you fill it right to the top with water?

Phantom water leakage problems from a waterfall that has no visible signs of spilling water.

You can have water leaking sideways and upwards from the pressure of water coming over a waterfall, travelling along little interstices (posh word!) between the liner and the cement and rockwork. Breaking the cement seal at the bottom of the waterfall can relieve this. Drill through very carefully or just crack the layer of cement with a cold chisel. Pipes laid in the bottom of the fall from the front of the liner to the outside front of the stonework would have done the job from the start.

If the pool leaks without the waterfall in operation it is obviously down to the pool liner.

Quite rapid leaks can occur when a flexible liner is laid so that a fold in the material works like a siphon. This is inevitable when the material is carefully folded up and over any support for the liner. When the water level is taken right up the point of overflowing, a primitive siphon effect is set off that does not cease until the water level drops to the bottom of the fold. The same can occurs when you have turf coming right down into the pool. When the soil outside the pool dries out (particularly after the pool had been over filled by heavy rain or topping up), little capillary reactions that had set themselves up in the soil below the turf, effectively siphoned the pool down to a level where the turf stops.

I have always used a rock edge to prevent this, but the problem caused by turf keeps cropping up year after year when people under the guidance of a TV programme or book, turf the pond edge right down into the water. There is also the fact that where things can siphon out, other chemicals can leach in to upset the pool balance. Not just lawn weed killers or fertilizers, but natural pollutants from the soil like the nitrates and phosphates (all like steak and chips to algae). The only effective way of preventing this is when you are building the pool, the liner must come up to the level required and dip down six inches into a shallow trench. In this I was told to lay a concrete sausage, but I would say myself that it ought to be clean gravel. This will help disrupt any siphoning action within the soil only because it has to bridge the trench.

Other causes of leaks can be holes in the liner caused by pets, children breaking ice and herons stabbing it.