Who says you need a pond to have a waterfall? With pondless waterfalls, the water goes into a basin that has a pump. We dig the basin and put in the liner. Then, we use Aquablox, which are like big plastic milk crates. They allow the basin to be 99% water but still support the rock and gravel on top.
Pondless systems are ideal for smaller spaces, or for folks who have no interest in fish. Maintenance on pondless systems is lower than for traditional ponds, too. You get the sounds and beauty of moving water without any added work.