## Formula for rate of evaporation of water

My sister and I are working on a project in which we need to know the rate of evaporation of water... I know that there are a lot of variables to this equation, but we aren't sure exactly where we will end up completing it, so does anyone know a formula to calculate the evaporation rate of water?

Also, if no one knows a good formula for it, I've come up with a list of variables which might possibly make a difference in the rate, but I'm not sure how much each matters. Can you tell me which of these actually makes a difference in the rate, and which ones don't affect it enough to worry about? The list we came up with was:

-heat (of the water)
-altitude (also air pressure)
-time
-speed of river/stream
-roughness of river bed (that would probably change the surface tension, causing a faster rate of evaporation)
-depth of water
-distance from equator (Water is a polar molecule, so would the magnetic fields of earth make a difference?)
-pollutants in water
-salinity
-mineral content (including heaviness of the minerals)
-humidity, and
-surface area

Thank you

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