A leaking pond: test the material before lining the whole basin

Before spending money on a pond liner, distinguish evaporation, leakage and overflow. Then test the proposed sealing material at a small scale. A material that briefly holds water in a bowl may not remain watertight through drying, roots and repeated filling.

Measure the loss

Mark the water level and record additions, withdrawals, rain and overflow. A nearby open reference container can help you think about evaporation, although its temperature and exposure will not perfectly match the pond. Look for wet patches outside the basin and inspect accessible fittings.

Match a liner to the site

NRCS guidance treats compacted soil and manufactured liners as designed systems. Suitability depends on soil properties, installation and protection. A clay-rich material needs appropriate preparation; simply scattering a little clay into sand is not the same as constructing a compacted liner.

Try a contained comparison

1. Use small perforated inner containers over separate watertight catch trays. Apply the proposed liner inside each inner container so seepage can be collected and measured.
2. Record the material, thickness and preparation method.
3. Compare collected seepage with an untreated container of the same design; use a separate watertight open container to help assess evaporation.
4. Observe more than the first fill, including a drying and refilling cycle where appropriate.

Plan the whole pond

Include safe access, overflow, animal protection and maintenance. If the pond will hold fish or food-production water, check material compatibility. For a substantial pond or embankment, obtain competent site-specific design advice before excavation. A household material test is only an early screening step.

Namibian climate and microclimate

High evaporation can disguise a successful liner, while drying cracks can undo an initially good seal. Namibia’s scarce water makes small tests particularly worthwhile. Consider whether a covered tank serves the intended purpose more efficiently than an open pond.