Tracing a leak

[allanb]

I've reason to think that I may have a leak somewhere in the pool system. I can't detect any significant leakage from the pool itself.

I have a pressure tank which can be fed from either the mains supply or a well. The pressure tank feeds a reservoir which is the source of water for the pool, and also some taps in the garden. There's no visible leak from any of these, although I suppose there could be a slow leak from some underground pipe which I haven't seen yet.

In order to check the tank, I've used the mains supply to build pressure in the tank to its normal maximum, which is around 3,3 bar, and then closed all the inputs and outputs. Since then, with the tank – in theory – completely sealed, its pressure has dropped by about 0,9 bar in 4 hours.

I assume that there's always some leakage in this kind of installation, but can anyone tell me whether this loss of pressure could be "normal"?

It has occurred to me that that the pressure drop may be caused by loss of air, rather than water (from the upper part of the tank, for instance.) But I'm not sure how to check this.

[Théière]

Poor over fairy liquid solution and wait for the bubbles?