Pond Seepage Loss & Where Your Water Goes

Seepage is the water that escapes a farm pond through its bed and banks into the surrounding soil, separate from evaporation off the surface. In an unlined pond on permeable soil it can be the single biggest loss, draining a useful share of your stored water before you ever pump it. Estimating it tells you whether lining is worth the investment.

Seepage loss = pond wetted area × seepage rate. The rate is a depth of water lost per day (mm/day), so multiplying by the area gives a volume per day. Over a storage period it compounds: total loss = daily loss × days. This tool does both, in cubic metres and litres, from your area and rate.

It depends entirely on the soil. Tight clay beds may lose only 2–5 mm/day, loams perhaps 10–25 mm/day, and sandy or fractured beds 50 mm/day or more. If you don't know your rate, measure the water-level drop over a still, cloudy day (to minimise evaporation) and subtract estimated evaporation, or use a soil-based estimate.

A liner puts a low-permeability barrier between the stored water and the soil. Compacted clay or bentonite reduces the bed's permeability; an LDPE or HDPE geomembrane nearly eliminates seepage. Cutting the rate from, say, 30 mm/day to 2 mm/day saves the bulk of the loss — the tool lets you compare rates to value the saving.

One cubic metre is 1,000 litres, and one millimetre of depth over one square metre is one litre. So a pond of 1,000 m² losing 20 mm/day loses 20 m³ = 20,000 litres a day. The tool reports the daily and total loss in both m³ and litres so you can relate it to your irrigation needs.

No. Evaporation is water leaving the surface as vapour and depends on weather and surface area; seepage is liquid water leaking through the bed and banks and depends on soil permeability and wetted area. Both reduce stored water — use this tool for seepage and the Pond Evaporation Loss tool for the surface loss.

For as long as you store water. A pond filled in the monsoon and drawn down through a dry season loses water every single day to seepage, so a modest daily rate becomes a large total over weeks and months. The tool's total-loss output over your chosen number of days makes that cumulative drain visible.

Compare the total water saved over the storage period against the lining cost and the value of that water for irrigation. On permeable soils with high seepage and scarce water, lining usually pays back quickly; on tight clay with low seepage it may not. The tool quantifies the water at stake so you can run that comparison.

They're sound planning estimates from area × rate × days. Real seepage varies with water depth, soil heterogeneity, the water table and how well a liner is installed, and the rate often changes as fine sediment seals the bed over time. Use the tool to size the loss and the lining benefit, then verify with a field drawdown test.