Building a garden pond with a liner: the project step by step, from marking it out to filling it with water

A pond dug by hand is a project within the reach of any reasonably motivated gardener: there is no need for an excavator or a builder for a pond of a few square metres. The most common and flexible technique is a liner pond: a tiered hole, a protective underlay, a watertight membrane, and you're done. Making your own garden pond with a liner comes down to seven steps: choose the location, mark it out, dig in tiers, calculate and lay the underlay and liner, fill it to shape the liner, finish the edges, then plant and let the water mature before adding any fish. This guide focuses on the work itself: the steps, measurements and pitfalls, in the order in which you will encounter them.

Step 1: choose the location

The location determines water quality for years. The criteria that really matter:

• The light: a few hours of direct sunlight per day, ideally in the morning, are enough for the plants to flower. A pond in full sun all day heats up and turns green more easily; a pond in complete shade stays cold and produces few flowers.
• The trees: avoid the immediate vicinity of large deciduous trees. Their leaves fall into the water and rot at the bottom, while their roots can damage the liner.
• The site: a low point in the garden may seem logical, but it collects runoff laden with soil and fertilizer. Choose a flat or slightly elevated site instead.
• Electricity: a pump or filter will require a power supply protected by a suitable residual-current device, installed in accordance with regulations (RGIE in Belgium). Our article on pond electrical installation explains the rules.
• The view: a pond is meant to be viewed from the terrace or a window. Place it where you will see it often.
• Underground utilities: check for pipes, cables, or drains before digging.

Step 2: mark out and size

Draw the shape on the ground with a garden hose or rope, then leave it for a few days: view it from the house and adjust it. Simple shapes with broad curves are easier to dig and cover with a liner without excessive creasing. Tight angles and narrow peninsulas make installation much more difficult.

As for dimensions, remember that a larger pond is paradoxically easier to balance: the volume of water buffers temperature and quality fluctuations. If you are hesitating between two sizes, choose the largest one your garden and budget allow. Then mark the outline with construction marking paint or dry sand.

Step 3: dig in levels

A successful pond is not a bowl-shaped hole, but a series of steps that accommodate different plants. Generally, there are:

First dig the entire outline to the depth of the first level, then move down to the next level, leaving a step at least 25 to 30 cm wide, and continue in this way to the bottom. Give the sides a slight slope rather than making them vertically sheer: the soil will hold better and the liner will be easier to lay. In sandy soil, make the slopes even gentler.

For plant placement by level, our article on planting depth in a pond explains how deep to place each type of plant.

The point most often missed is the edge level: if the perimeter is not horizontal, the liner will show on one side and the water will overflow on the other. Check it with a long plank and a spirit level, or a water level (a transparent hose filled with water), going all the way around. Correct it by adding or removing well-compacted soil.

Keep the topsoil separate: it will be used in the beds around the pond. The soil from the bottom, often clayey, can form a slope or a small mound for a waterfall.

Step 4: prepare the bottom and lay the fabric

Run your hand over the entire surface of the hole: remove stones, roots, pieces of glass, or brick. A sharp stone beneath a liner will inevitably puncture it under the weight of the water. On stony soil, spread 3 to 5 cm of sand over the horizontal bottoms.

Then lay the geotextile fabric over the entire surface, overlapping the strips by about twenty centimetres. It protects the liner from underneath and also limits rodent damage. On the banks where stones will be placed, a second layer of fabric over the liner provides good extra protection.

Step 5: calculate and lay the liner

The calculation

The classic formula for a stepped pond:

• liner length = maximum pond length + 2 × maximum depth + approximately 1 m of margin (50 cm on each side for anchoring);
• liner width = maximum width + 2 × maximum depth + approximately 1 m of margin.

Measure the maximum length and width along the bottom of the hole with a flexible tape measure; it is even more reliable to measure directly along the developed length, then simply add the margin.

PVC or EPDM?

PVC is economical, lightweight, and easy to fold, making it well suited to small and medium-sized ponds. EPDM, a synthetic rubber, is more flexible in cold weather, more resistant to UV rays, and significantly more durable, but heavier and more expensive. For a large pond or a project intended to last a very long time, EPDM is generally the best choice. Our comparison for choosing your pond liner provides details on thicknesses and uses.

Installation

1. Choose a mild day: a cold liner is stiff, while a liner warmed by the sun is much easier to work with.
2. Unroll the liner beside the hole, then have several people slide it over the hole without dragging it across the ground.
3. Let it descend into the hole without stretching it: it should conform to the shelves under the weight of the water, not through the force of your arms.
4. Temporarily weigh down the edges with a few smooth stones or sandbags.
5. Walk barefoot or in socks on the liner to adjust it on the steps.

Step 6: fill and form the folds

Filling puts the liner in place. Do it gradually, staying nearby:

• fill by a few centimetres, then adjust the liner at the bottom;
• as the water rises, gather the unavoidable folds into a few large, regular folds rather than a multitude of small wrinkles;
• gradually release the weights along the edges so that the liner descends without becoming taut;
• never cut off the excess until the pond is full and the liner has settled, ideally after 24 to 48 hours.

Tap water is suitable for the initial filling. For summer top-ups, rainwater is often preferred. Our article on which water to use to fill a pond compares the options.

Step 7: finish the banks

The finishing of the edges makes all the difference between a “liner hole” and a pond that looks as though it has always been there. Three rules:

• Raise the liner vertically behind the edging, above the water level, to create a barrier. Otherwise, garden soil draws water from the pond by capillary action, and the level drops without any visible leak.
• Hide the liner: overhanging flat stones, pebbles, gravel-covered liner that becomes covered with moss, or bank plants that trail into the water.
• Provide access: a large, stable flat stone or a small gently sloping pebble beach allows birds to drink, hedgehogs and frogs to get out, and you to carry out maintenance.

Finally, cut off the excess liner, leaving a margin of at least 20 to 30 cm buried or tucked under the stones.

Planting and letting the water mature

Plants are the best ally for clear water: they consume the nutrients that algae feed on and provide shade. As a rule of thumb, aim to shade one-third to one-half of the surface with floating leaves (water lilies) or marginal plants, and add a few submerged oxygenating plants. Plant them in baskets filled with poor soil or special aquatic-plant compost, never enriched all-purpose compost.

Choose native or non-invasive ornamental species. Several aquatic plants once commonly sold in garden centers, such as Brazilian watermilfoil, large-flowered water primrose, and lagarosiphon, are now banned from sale and planting in the European Union under the regulation on invasive alien species.

The pond will then go through a phase of green or cloudy water for a few weeks: this is normal, while the plants become established and bacteria colonize the surfaces. Do not empty everything at the first sign of algae.

Filtration: necessary or not?

A pond planted only, without fish or with very few small fish, can function without a filter if it is large, deep, and well planted enough. As soon as you want numerous fish, clear water in midsummer, or a small pond in the sun, a pump and filter become necessary. Complete kits combining a pressure filter, pump, and UVC lamp are the simplest solution for a small pond: the filter can be half-buried in the pond edge and return the water via a small stream.

A realistic schedule

For a pond of a few square meters, dug by hand, allow roughly:

• one weekend for marking out and digging (longer in clayey or rocky soil);
• one day for leveling, cleaning the bottom, laying the underlay, and installing the liner;
• one day for filling, finishing the edges, and planting;
• then wait patiently for a few weeks before introducing any fish.

The best seasons are spring and early autumn: the soil is soft, the liner is easy to work with, and the plants establish quickly.

Mistakes to avoid

• A pond that is too small and too shallow, which heats up in summer and freezes to the bottom in winter.
• Non-horizontal edges, which leave the liner visible.
• Forgetting the protective felt on rocky ground.
• A liner stretched during installation, which tears or pulls away from the sides as the pond is filled.
• Excess liner cut too early.
• Enriched potting soil in the baskets, which feeds algae for months.
• Fish introduced as soon as the pond is filled.

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Frequently asked questions

— How do you calculate the liner size for a pond?

Add twice the maximum depth to the pond's maximum length and width, then approximately 1 m of allowance (50 cm on each side) for anchoring the edges.

— How deep should a garden pond be?

Plan for levels: a wet zone from 0 to 20 cm, a bank zone from approximately 20 to 40 cm, and, if possible, a deep zone of at least 80 cm for water stability and overwintering fish in Belgium.

— Should sand or felt be placed under the liner?

A geotextile felt is recommended over the entire surface, optionally supplemented by a few centimeters of sand on rocky ground. It protects the liner from stones, roots, and rodents.

— When can fish be added to a new pond?

After a few weeks, once the plants are established and the water has stabilized. Then introduce fish gradually, in small numbers.

In summary

• Location: a few hours of sunlight, away from large trees, outside low-lying areas, with compliant electrical installations.
• Digging in levels and perfectly horizontal edges.
• Liner = maximum dimension + 2 × depth + approximately 1 m of allowance, laid on protective felt.
• Gradual filling with large, regular folds; excess cut only when the pond is full.
• Banks that rise above the water, native or non-invasive plants, and patience before adding fish.

Last updated: October 3, 2026.