Our pool has been working perfectly for a long time - and I’ve been surprised and delighted that we’ve not had the algae, etc, problems I know others have had this year - but a few days ago the water level dropped pretty rapidly by about 5 centimeters, then stabilised again.
There is no visible evidence of any leak, and indeed everything appears to be working normally, including the automatic fill (though it’s quite slow so obviously didn’t immediately compensate for the sudden loss).
The obvious explanation, I know, is a sudden breach in the buried pipework, and this is certainly possible given the level it dropped to - and I have ordered an inspection camera to have a look - but I wonder if any pool owners here have any other insights/advice?
Turn off the autofill until you are sure. I had a customer with a long standing leak, a large water bill and they simply didn’t know.
Have you had any thoughts about possible causes/remedies John? (Apart from my pipework leak / inspection camera idea)
Geof, I have not been given much to work on. If you have turned off the autofill where has the level stopped dropping? Any obvious things like just at the bottom of the skimmer or return fittings?
Pool shops sell bungs for a round €1.5 start bunging up the holes for the skimmer and returns and see if the level stops falling. take out one bung at a time and see if it starts again, that will let you know if it’s plumbing.
Thanks John - I’ve actually already gone this far now - it looks very likely that it is indeed a problem at the bottom of the skimmers, or possibly at a hidden joint with the pipework to the bottom drain, which is probably at the same level.
My inspection camera should arrive any day so hopefully this will allow me to pinpoint it exactly.
sounds exciting. OH has a camera to inspect inside the fuel tanks of his cars and any other nooks and crannies… also used it to checkout what was behind an old wall (just drilled a small hole) sadly no hidden treasure. 
A very common point for issues. Too many pool builders concrete the skimmer in place and ground movement simply pulls it apart.
Not a fan of bottom drains, they don’t do much.
Bottom drains should be run in their own pipe back to the pump and not sharing the second port in the skimmer.
We have a Debordement/ overflow pool, hence no skimmers, late summer, we noticed that we were using loads of Ph and that our auto water refil was operating more than before, and had to top up every day by more than a few cms. So when time came to winterising, we investigated the drop in water. Had a local company come out and check it out with sound. And camera equipment, thry could not vonfirm if their was a leak from any if the pipework. They were unable to test/check the overflow partof the pool, as they did not have the correct equipment,. Trying to find someone to check for a leak was not apparent, but after many phone calls, got lucky, have arranged an appointment for 20 nov, and the guy will arrive, only if it is not raining.
So fingers crossed for good weather, and a succesful solution to our leaky pool.