Which product should I choose to waterproof my garden pond? Liner, EPDM, prefabricated shell, concrete, or polyester

When you build a pond, the question of waterproofing comes up very quickly, and with it a flood of conflicting opinions. "Go for EPDM, it lasts forever." "A preformed pond is simpler." "Nothing beats concrete." They are all right, in certain situations. There is no single best waterproofing product: the right choice depends on the shape and size of the pond, your budget, the time you want to spend on it and whether demanding fish such as koi will live in it. This guide compares the main options to help you decide.

The five main options

Criterion 1: the shape of the pond

A free-form pond, with shelves and sloping banks, calls for a flexible liner. EPDM excels here: it folds without cracking and forms creases that are easier to spread out. A rectangular pond with vertical walls, raised or built against a terrace, is better suited to rendered concrete or polyester, which give clean corners without folds. For a small pond of a few hundred litres, a preformed pond is often the simplest route.

Criterion 2: the budget, over time

At purchase, PVC is the cheapest, followed by EPDM, then masonry or laminated solutions, which require more materials and labour. But compare over time as well: a cheap liner that stiffens and has to be replaced means draining the pond, removing the plants and redoing the edges. The real cost of waterproofing is above all the cost of redoing the work the day it fails: saving on the liner of a large pond is rarely a good calculation.

Criterion 3: the fish

For an ornamental pond with a few goldfish, every solution works, provided the products are designed for pond use. For koi, keepers often look for smooth walls without folds where waste accumulates, easy to clean and compatible with bottom drains: rendered concrete or polyester then have the edge, even though many koi ponds built with well-laid EPDM work perfectly.

One precaution applies to every option: a building product is not necessarily safe for fish. Liners, adhesives, renders and resins must be explicitly intended for ponds, and cement-based or freshly laminated surfaces need curing time and rinsing before fish are introduced.

Criterion 4: installation and repairability

A liner can be laid in a day with a few helping hands. Its success depends on preparing the ground (stones and roots removed), the protective underlay and a careful edge that stops water escaping by capillary action. It can be repaired with patch kits or tapes suited to the material. Concrete and polyester require more know-how, but can be repaired locally. A preformed pond repairs well if it is made of polyester, much less easily if it is polyethylene.

Three typical scenarios

• Small decorative pond, tight budget: PVC liner on underlay, or a preformed pond.
• Free-form ornamental pond, from a few m³ to a few dozen m³: EPDM on underlay, the best compromise between flexibility and durability.
• Koi pond with straight walls and bottom drains: concrete with a suitable waterproof render, or laminated polyester.

What matters as much as the product

Most of the leaks we see in practice do not come from a poor product but from a rushed installation: liner laid without underlay on stony ground, liner edge too low so water escapes, badly made pipe penetrations, a waterfall without continuous waterproofing. Whatever system you choose, take the time to prepare the base and finish the edges carefully: that is where the lifespan of your pond is decided.

Read also

To go further on flexible versus rigid: Liner or polyester for my garden pond?.

READ THE ARTICLE

Read also:

• Renovating an old garden pond: diagnosis, repair or rebuild
• EPDM liner: calculating and ordering the right size

Frequently asked questions

— What is the most durable liner for a pond?

EPDM is known for its flexibility and durability. PVC costs less but stiffens over time, especially when exposed to UV.

— Is a preformed pond or a liner better?

A preformed pond is quick to install for a small pond with a fixed shape. A liner gives more freedom of shape and volume.

— Which waterproofing system for a koi pond?

Rendered concrete or laminated polyester for smooth walls and bottom drains; well-laid EPDM also suits many koi ponds.

— Do you always need underlay under the liner?

Yes. Geotextile underlay protects the liner from stones, roots and friction; it is inexpensive insurance.

In summary

• No product is best everywhere: it all depends on shape, budget and use.
• PVC: affordable and repairable; EPDM: flexible and durable.
• Preformed pond: quick for small ponds; concrete or polyester: straight walls and koi.
• Compare the cost over time, not just at purchase.
• Products designed for ponds, underlay under the liner, careful edges.

Last updated: 29 September 2026.