Consistent leak for several years

[bobinct]

I live in Northeast and have an inground concrete pool which has lost about 3/8 inch water/day during summer. Does this seem excessive ? Tried die tests without any sign of leaks. Does it make sense to have lines pressure tested? If there is a leak in one of the lines, can it/they be repaired without digging up and/or breaking thru deck?

[ChuckGeo]

The first thing you want to do is take water loss measurements, 24 hours with the pump on and 24 hours with the pump off. If the measurements are the same you probably don't have a plumbing leak. If you loose more with the pump on, suspect the return line, if less loss with the pump on suspect a suction line - skimmer or main drain. If it looks like a plumbing leak you'll have to get the suspect line pressure tested to confirm it. Unfortunately, I know of no way to repair a leak in underground plumbing without digging it up and cutting out the leak and replumbing.
However, a small leak, 3/8" per day, is probably non plumbing and should be locatable with a dye test. The trick is to put the dye at the right place. Look at the skimmer body and the skimmer throat where the skimmer butts up to the pool, around all of the wall fittings (esp. underneath the fittings), light niche and conduit, main drain sump and any cracks in the structure of the pool. A leak this size can be tough to find, make sure the pool is totally still when you do your dye test.