Ponds don't have to be dug in the ground. A formal pond with a raised edge using bricks or concrete facing blocks makes wonderful waterside seating. Raised ponds are also much safer if there are small children around, especially if you construct the edging about 450-500mm (1ft 6in-2ft) high.
The water must also be clear and to achieve this you will need to install a pump to recycle the water, or establish a careful balance of pond life, which includes oxygenating plants (at least 10 per square meter of water surface), snails and fish. A successful balance creates a food chain, which excludes the green algae that stains surfaces, clouds the water and kills pond life.
The best way to construct a raised pond is to use a low, double-skin construction for strength and to make sure it is watertight in case of leaks in the liner. The inner skin can be constructed of plain concrete blocks (decorative bricks or blocks can be saved for the exterior walls). Build the walls with a space between that matches the width of the coping stones used to finish the top of the walls. You will need to lay good solid foundations to support the walls, so lay footings of 100-150mm (4-6in). Raised ponds can be lined using a made-to-measure prefabricated rigid liner, which reduces the number of creases at the corners that you will have if you opt for a flexible plastic liner, but these often don't have overflow or outlet facilities. The top edge of the liner is trapped under coping stones making it invisible.
