The first thing that needs to be done is to pick an area for your water garden. Certain considerations need to be thought of- you will want to choose a level sight in full sun that is free from overhanging trees and has easy access (as easy as you can make it, just the further it is the higher your wiring cost) to the house for electrical connections. Once you do that you’ll want to examine your liner and move it around the area until you like how it looks. Notice the liner (most liners) has two depths, a deep depth, and along the sides some areas of shallower depth, called shelves. Place the liner on the ground where you like it and using marking paint or flour mark out the outline of the deepest part only; this is where you must dig.
Source: Backyard Gardening Blog