Where you site your new water garden may be strictly limited. But you will want it where you will see and experience it most readily - alongside a patio or near the screen house. Ideally, it will also be visible from inside the home.
If you plan to fill your pool with colorful water lilies and other flowering plants (see below), see that the pool gets at least six hours of sunlight a day. On the other hand, shaded pools are still attractive and color can be added by setting shade-loving plants such as impatients immediately alongside the pool.
For easiest construction the site should be level.
Rigid preformed plastic or fiberglass ponds are available, but the hole has to be carefully dug to accept the pool. By far the simplest (and least expensive) approach is to use a flexible liner made of synthetic rubber or PVC.
Simply dig the hole, place in the liner, and fill with water. The weight of the water will mold the liner to the shape of the hole. Line the hole first with any material that will protect the liner from protruding sharp stones of sticks. Special liner material can be purchased but old carpeting will do and so will newspapers laid a dozen or more sheets thick.
Outline the shape of your pond with a piece of thick rope or length of hose and begin digging. Leave a rim about 10 inches deep all around the edge of the pool. This creates a shelf on which the potted water plants will stand. Dig deeper in the center to give the toads and fish swimming room.
Size and depth
Larger is better than smaller because the more water you have in your pool, the less it will fluctuate in temperature, overheating in summer, icing up prematurely in winter. Broad-leafed plants like water lilies and floating water hyacinths also do much to keep summer temperatures down.
If you plan to cover winter fish, part of your pond must be at least two feet deep. In most areas of the US, this depth leaves enough unfrozen water for the fish to retreat to in winter. Having a pump circulating some of the water also helps keep some of the pond open and the water oxygenated in winter.