Evaporation involves the change in state of a liquid to a vapour. The evaporation rate from salt-water resources depends mostly on saturated vapour pressure above its surface. On the other hand, the saturated vapour pressure is affected by the ion activity coefficient, which stems from the chemical salt concentration of water. Thus, an increase in concentration of water results in a reduction of saturated vapour pressure. In order to acquire the actual rate of evaporation from salt-water resources, a uniform set of evaporation pans with different but specified salt concentrations were used, in a meteorological station under the same conditions. The difference in evaporation rate of each pan can only stem from the difference in chemical salt concentration and, indeed, the molar fraction of water in each saline solution. Therefore, by applying the water molar fraction in the pressure term of fresh-water evaporation measurement formulas, these equations were developed further for determination of evaporation rate from salt-water resources. The proposed formulas using very simple terms seem to be suitable for determination of evaporation rate from any water (typically saline, semi-saline and fresh water) with a satisfactory precision. Copyright © 2007 John Wiley & Sons, Ltd.