Pond Evaporation Rate Calculator
Standard (Meyer's Equation)
Arid/Dry Climate Adjustment
Estimated Daily Evaporation
Water Loss: 0.00 inches per day
Total Volume Lost: 0.00 gallons per day
Weekly Total: 0.00 gallons per week
How Pond Evaporation is Calculated
Pond evaporation is a complex thermodynamic process driven by the difference in vapor pressure between the water surface and the surrounding air. While many pond owners assume heat is the only factor, humidity and wind speed often play much larger roles in daily water loss.
Our calculator uses a modified version of Meyer's Law, which considers:
- Saturation Vapor Pressure: The pressure exerted by water vapor at the pond's surface temperature.
- Actual Vapor Pressure: The amount of moisture currently in the air (calculated from air temperature and relative humidity).
- Wind Factor: Wind moves saturated air away from the surface, allowing more water molecules to escape.
Realistic Example:
If you have a 1,000 sq ft pond on a typical summer day (85°F air, 78°F water, 50% humidity, and 5 mph wind):
If you have a 1,000 sq ft pond on a typical summer day (85°F air, 78°F water, 50% humidity, and 5 mph wind):
- The evaporation rate is approximately 0.18 inches per day.
- This results in a loss of about 115 gallons of water every 24 hours.
- Over a week, that's over 800 gallons of water vanished into the air!
Key Factors Influencing Water Loss
1. Humidity: High humidity (like in Florida) slows down evaporation because the air is already saturated. Low humidity (like in Arizona) acts like a sponge, pulling water out of the pond rapidly.
2. Wind Speed: Wind is often the "silent killer" of pond levels. A constant breeze significantly increases the rate of evaporation by preventing a localized "humidity dome" from forming over the water surface.
3. Water vs. Air Temperature: If the water is significantly warmer than the air (common in early autumn nights), the evaporation rate spikes as the warm water attempts to reach equilibrium with the cooler, drier air.
Is My Pond Leaking or Just Evaporating?
To determine if your water loss is normal, perform the "Bucket Test":
- Fill a bucket with pond water and place it on a step in the pond (so it's at the same temperature).
- Mark the water level inside the bucket and the pond level on the outside of the bucket.
- Wait 24-48 hours. If the pond level drops significantly more than the bucket level, you likely have a leak. If they drop at the same rate, it is purely evaporation.