mystery of missing water solved
 

Taking the advice offered, I removed a few large rocks along one side
of the waterfall to see if there were any leaks or cracks in the
liner. You were all right. The loss of water could not possibly be
due to just evaporation.

Some water was taking a detour. So I just hope the guy honours his
work and returns my call.

Thanks to all. Great ng!

Larry
Southern Ontario