Pond Liners

A pond liner is the waterproof barrier between the ground and the water, sized larger than the finished pond so it can be trimmed and tucked in at the edges rather than stretched to fit exactly. Getting the size right before ordering matters more than almost anything else in a pond build, since a liner that's too small can't be extended once it's in the ground.

To measure, add twice the pond's maximum depth to both its length and width, then add another foot or two on each dimension for overlap at the edges. Rectangular ponds are straightforward to calculate this way; irregular shapes should be sized to the pond's longest points in each direction.

EPDM rubber is the standard material for durability and flexibility, and it's usually sold in the pre-cut size closest to, and slightly larger than, the calculated dimensions. Underlayment or old carpet is typically laid beneath the liner to protect it from rocks and roots, and is worth budgeting for separately even when it isn't sold alongside the liner itself.