On 30/06/2020 18:31, Jeff Layman wrote:
Once the lined pond is full of water, it won't make any difference if
rainwater gets behind the liner as the pressure inside and out will be
equal.

Our rather badly made pond gets water behind the liner. On occasion
there have been big bulges, which is a PITA because once the ground
water has dropped - which doesn't usually take more than a few weeks -
the pond is only half full. Despite all the rain.

Andy
--
Redoing it is on the must do that one day list.