The most important task while building a pond is installing the pond liner and its underlayment. The liner and underlayment is just like the foundation of a building. The underlayment helps to prevent punctures, rips, and tears in the pond liner caused by rocks, stones, roots, etc. The pond liner prevents the water from seeping into the surrounding ground. A liner is necessary even for those areas that have soil rich in heavy clay.

Pond liners come in a variety of materials, prices, shapes and sizes:

• Preformed liners are best suited for small water garden features and are quick and relatively easy to install.
• Flexible EPDM (Ethylene Propylene Diene Monomer – a synthetic rubber) pond liners are suitable for medium to large ponds, and are considered among the best flexible pond liners.

Be sure to use a liner specifically designed for ponds. Many alternative liner materials that people try to use are not resistant to ultraviolet light, break down quickly, and are toxic to fish.

Installing pond liners is a delicate task, as they may receive holes and tears caused by sharp objects like stones or roots. It is important to remember to install underlayment between the liner and the soil. If you do not, you run the risk of a leak. If you do get a leak or need to extend your existing pond, seam kits are available