Evaporation & Makeup Water Calculator
Screen pond or basin water loss before local climate, liner, pump, and permit review
Free evaporation and makeup water planning screen for pond owners, municipal operators, and environmental engineers who need a transparent first-pass estimate of water loss. Enter surface area, average depth, evaporation rate, pan coefficient, wind exposure, liner/seepage assumption, precipitation, water cost, and operating hours. The output shows daily evaporation, seepage, rainfall credit, net loss, a 12-month projection, and makeup-flow demand. The app includes source-gap warnings because the climate presets, seasonal distribution, wind factors, seepage rates, and rainfall retention are local placeholders, not a site water-balance study, NOAA station lookup, seepage test, pond or lagoon design, water-rights review, permit design, pump sizing, or pipe sizing.
Screen pond volume and average fill/drain timing
Pond Fill/Drain Source Screen →Screen lagoon planning inputs for wastewater treatment
Lagoon Planning Screen →Size irrigation pump and pipe for makeup supply
Irrigation Pump & Pipe Calculator →Screen pump energy-cost prompts for makeup water delivery
Pump Energy Source Screen →How It Works
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Enter Pond Surface Area
Enter the water surface area in square feet or acres and the average depth used for the volume comparison. For irregular ponds, use measured survey, GIS, drone, or mapping data when decisions depend on the result.
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Select Climate or Enter Local Data
Choose a climate preset for screening or select Custom and enter local pan, lake evaporation, ET, or water-balance data. The app applies the entered pan coefficient and wind factor, then distributes annual evaporation with a fixed seasonal curve.
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Choose Liner and Seepage Assumptions
Select a liner type to load a generic seepage placeholder or enter a measured seepage rate. Verify liner behavior with soil, groundwater, compaction, leakage, seam, puncture, cracking, and geotechnical data where it matters.
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Review the Source Gaps
Use the monthly projection and makeup GPM as a planning screen. Then reconcile climate, seepage, rainfall, runoff, overflow, groundwater, water source, pump, pipe, power, treatment, discharge, permit, and water-right assumptions.
Built For
- Pond owners screening whether evaporation or seepage may explain water-level drops
- Municipal lagoon operators preparing a first-pass makeup-water budget before engineering review
- Environmental engineers documenting assumptions that still need local water-balance data
- Aquaculture operators estimating summer makeup demand before source and permit review
- Golf course or irrigation operators comparing rainfall, seepage, and makeup-cost assumptions
Assumptions
- Evaporation is estimated from the entered rate using the entered pan coefficient and wind exposure factor.
- Seepage rates are generic placeholders for each liner type and do not validate actual site leakage.
- Surface area is assumed constant (no significant change in area as water level drops from losses).
- Rainfall credit assumes precipitation falls directly on the pond surface and is retained.
Limitations
- Does not model the effects of pond depth or water temperature on evaporation rate beyond the wind exposure factor.
- Does not account for runoff inflow or groundwater contributions to the pond water balance.
- Does not model seasonal groundwater table fluctuations that affect seepage rates.
- Does not calculate pump, pipe, electrical, intake, backflow, treatment, storage, spillway, outlet, discharge, or infrastructure requirements.
- Does not determine permit, water-right, wastewater, stormwater, environmental, dam-safety, or regulatory requirements.
References
- FAO Irrigation and Drainage Paper 56 - pan evaporation and pan-coefficient source context.
- NOAA NCEI U.S. Climate Normals - station-based precipitation and climate-normal source context.
- NRCS Pond Sealing or Lining Compacted Soil Conservation Practice Standard 520 - seepage and lining source context.
- Local survey, weather, groundwater, soil, liner, operating, permit, and engineering data remain required for design use.
Frequently Asked Questions
Learn More
Pond Evaporation & Water Loss: Calculating Makeup Water Needs
How to estimate pond evaporation, seepage by liner type, seasonal water budgets, and required makeup water flow rate and annual cost.
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