There are three basic types of ponds.  Preformed, flexible liner, and concrete.  Each has a description below.  Our source for this information has been from: “The Complete Pond Builder” by Helen Nash, copyright 1996, Sterling Publishing Company.

Preformed ponds, usually made of strong plastic such as ABS, Acrylonitrile Butadiene Styrene polypropylene or HDP, high density polythene, or fiberglass, are commonly available and easy to install. Although some are as large as twelve feet across, most are smaller, usually three to six feet across and 18 inches in depth.  They very smallest are commonly only 12 inches deep.  Being so shallow as well as so small, they may encounter problems with fluctuating water temperatures (which can stress fish) and with limited surface area (seriously limiting oxygen available for fish).  It is very important with small preformed ponds to keep the number of fish lower than normally recommended maximum stocking rate.

Plastic compositions cost less than fiberglass-reinforced or fiberglass constructions, but will not last as long.  They may turn brittle, cracking and deteriorating within a few years.  Even though the pond itself may be under warranty, the prospect of labor and the expense of dismantling and replacing the ponds after only a few years may offset the greater cost of a stronger pond form.

Another factor to consider when selecting a preformed pond is the strength of the top edge.  Because heavy rocks or paving that rest on a plastic edging may buckle and crack the side walls of the pond, reinforcing the top edge may be a good idea.  A concrete foundation, as well, may be wise.  Fiberglass generally will not require such reinforcement, although it may still be desirable, to provide pond-edge stability.  To avoid frustration and unnecessary expense if a plastic pond is chosen, be sure the top edge is level and not warped.

Preformed ponds are available in a variety of standard forms.  Many offer planning shelves. In selecting one of these ponds, be certain the shelf is wide enough for a potted plant.  Surprisingly, many such shelves are too narrow to be functional. Fiberglass ponds, though more expensive, can be designed and constructed to specification, thereby offering the opportunity for relatively simple installation. 

If any one product can be credited with revolutionizing water gardening, it would have to be the flexible liner.  Although some enthusiastic would-be-water gardeners have used the least expensive and most readily-available materials, such as thin plastics or swimming pool linters, these linters are not suitable for water garden ponds.  Even heavier grades of plastic sheeting puncture easily and degrade quickly, often in less than three years.  Vinyl swimming pool linters may be treated with algaecides that prove toxic over time to fish and plants.  Also, their light color appears artificial.

In the past, PVC linters were commonly used for water gardens.  More durable than plastic sheeting, they could be expected to last 10 to 15 years.  However, they needed special care to protect hem from the degrading UV sunlight.

While butyl was the liner of choice, offering elasticity, durability, and stability, it was expensive.  However, Firestone Rubber Company in the United States developed a comparable synthetic rubber sheeting, EPDM, ethylene propylene diene monmer, commonly called PondGard.  This black, flexible liner with a 50 year life expectancy offers the same positive qualities of the butyl and is prices competitively.

Although the development of strong, flexible EPDM-type liners have virtually replace the idea that a long-lived pond  must be constructed of concrete, concrete may still be the construction method of choice.  Successful concrete ponds, particularly large ones, are best constructed by professionals.  The do-it-yourselfer should start out with a small concrete project, such as a fountain basin or a small water feature.

Concrete is made of specific amounts of cement, sand, gravel, and water.  Mortar is similar but has no gravel in the mix.  Both may be purchased premixed in 80-pound bags.  Each makes up 2/3 cubic foot.  Water is the catalyst that causes the material to harden; the less water, the stronger the mix and the stiffer it is to work. 

A good stiff mix, well-tamped, is primary.  Weather is a critical factor: freezing conditions invite disintegration of the concrete before it has cured, and very hot conditions may allow it to dry too quickly, likewise resulting in a weak, disintegrating product.  Use acid-resistant cement in very acidic soil to prevent disintegration.

Concrete work should use reinforcing mesh, or in larger or steep-sided areas, reinforcing rods and expansion joints.  Bury such reinforcements inside the concrete at least one inch from the outer surface.  Any overlapping reinforcements should be tied together with wire.