The most popular choice for advanced pond constructions is the pond liner, because it offers an unlimited potential for design creativity, dependable longevity, and low maintenance. However, make sure you invest in a high quality pond liner, because a low-quality liner may leak, be toxic to marine life, and/or cause many other headaches in the upcoming months after your installation.

The purpose of a liner is to retain the water within the pond basin, while providing the water gardener with the complete flexibility of shaping his/her own pond design. Durability is one of the primary yardsticks used to measure the efficacy of pond liners. In areas where earth tremors occur, liners do not crack as easily as preformed liners or concrete, and will thereby last longer than their preformed cousins. However, depending on the liner material, liners are adversely affected by UV light to varying degrees.

A secondary consideration is the suitability of the liner material towards marine life. Plastic-based liner material (E.g. polyethylene, polythylene, PVC, and polypropylene) contain stabilizers which allow the plastic to bond. In liner materials such as polyethylene, polyethylene, and PVC, these stabilizers are lead- and barium-based, which are heavy-metals that are known as carcinogens. Another liner material, Polypropylene, utilizes Di-Octyl Phtalate (DOP) as a stabilizer, which is a toxic substance that is extremely corrosive and harmful. Envision what would happen to your aquatic life if a crack were to develop in a plastic liner, and plasticizer were to enter the pond eco-system.

There are five main types of liner constructions: Polyethylene, Polythylene, PVC liners, EPDM/rubber, and polypropylene. Polyethylene and Polythylene liners typically cost half that of polypropylene and EPDM. While they are both lightweight and inexpensive, they typically only last one season. Polyethylene will readily conform to any shape, however, it does not have the sturdiness that is required for a permanent pond liner. Polythylene, on the other hand, is extremely rigid and can be stiff to work with. Polythylene can be damaged easily by rocks, and has to be handled with care. If polyethylene is damaged, it cannot be seamed together without expensive welding equipment.

PVC and PVC-E liners are the next step up from polyethylene and polyethylene, and they can last for up to 10 years. Compared to other liners, PVC is somewhat more affordable, while being somewhat puncture resistant at the same time. In terms of durability, the typical 20-mil (I.e. 0.020) thick PVC is somewhat mediocre; liners need to last a significant amount of time, because no water gardener wishes to replace their pond liners with any frequency. Therefore most water gardeners opt for liners that can last at least 20 years.

Polypropylene is an expensive material, however, it is the most durable pond liner material in existence because it can last for up to 40 years. Polypropylene, however, is not as flexible as EPDM liners. The main advantage of polypropylene is that it comes in large sheets larger than 50 x 100. If you are building an extremely large pond, polypropylene may be a viable option. Otherwise, the majority of pond builders prefer EPDM rubber liners.

EPDM (Ethylene Propylene Diene Monomer) rubber liners are recommended for most pond installations because of their delicate balance between longevity, flexibility, affordability, and their lack of toxic plasticizers. Because EPDM liners are rubber-based, they are extremely flexible (much more so than PVC liners), and they do not contain any plasticizers that can make the liner brittle and crack with age. The lack of plasticizers also makes them completely fish and aquatic safe.

The extra flexibility of EPDM comes in handy when working with irregular folds and shelves that are commonly found in a pond. While more expensive than Polyethylene, polyethylene, and PVC liners, a 45-mil EPDM liner can last for up to 20 years because of its natural resistance to UV, and its puncture resistance. However, a limitation of EPDM is its size; they typically arrive in sheets ranging from 5 x 10 to a 50 x 100 roll. With some training, landscapers should be able to join small sections of EPDM liner with seaming tape.

EPDM rubber liner is currently the standard liner for most water gardening installations. However, before you go out and buy an EPDM liner, make sure you do the prior calculations to determine how much liner you need. A handy calculator that can be used to calculate the required EPDM liner size can be found at http://www.gardensupermart.com/tips/calc.asp