Evaporation of water from a water surface depends on water temperature, air temperature, air humidity and air velocity above the water surface.

gh = Θ A (xs - x)

where

gh = amount of evaporated water per hour (kg/h)

Θ = (25 + 19 v) = evaporation coefficient (kg/m2h)

v = velocity of wind above the water surface (m/s)

A = water surface area (m2)

xs = maximum humidity ratio of saturated air at the same temperature as the water surface (kg/kg)  (kg H2O in kg Dry Air)

x = humidity ratio air (kg/kg) (kg H2O in kg Dry Air)

Note! The units for Θ don't match since the this is an empirical equation - a result of experience and experiments.