Choosing Water Feature Materials
When choosing and planning your water feature, make sure that it fits in with the composition of your garden, perhaps using materials that feature elsewhere in the design.
From: DK Books - Garden Design
Waterproof masonry, such as concrete, will seal in the water in your feature, whether it is a raised or sunken pool. Any material with joints, such as bricks, will leak, so add a specialized render to the inside of your pond, which can then be colored or clad with tiles; alternatively, line it with a waterproof membrane such as polyethylene or PVC. Take care not to add any decoration that could puncture the waterproof layer or liner, and ensure that any joints where pipes enter the pool are fully watertight.
Covering the edge of a pond liner with flat stones will protect it, but ensure that they are smooth-edged to prevent punctures.
Edging and Lining Streams
Natural-looking water features, such as artificial streams or wildlife ponds, are usually irregularly shaped, and lined with flexible waterproof materials. Ensure that the pond is deep enough in places to allow the required rooting depth for your chosen aquatic plants. Streams require a "header pool" or reservoir at the top of the slope, into which water is pumped from the lowest pool. Cover the edges of your pool or stream with planting or flat stones to conceal the waterproof membrane.
This artificial pond is on two levels and has been lined with a membrane covered with flat stones; large stones overhang the edge of each level to protect the liner from damage and to create mini-waterfalls.