We usually recommend that customers turn off their waterfall and watch the water level in the pond. If the water does not go down at all, then the leak is probably in the waterfall itself. Try using waterfall foam to close gaps in the rocks and direct the flow of the water down the waterfall instead of off to the side. If the water level does go down, it will stop below the area with the leak. Check all the edges of the pond for run off. Look for folds in the liner where water could be running out of the pond.
