The possibility of estimating groundwater inflow to irrigation drains in Minia, Egypt, using stable isotopes has been explored. The evaporation pan technique described here makes use of small variations in the concentration of naturally occurring stable isotopes (oxygen-18 and deuterium) in irrigation-fed groundwater and surface water as well as agricultural drainage water. The agreement between the stable isotope pan experiments carried out at Minia with others conducted at different locations in Egypt makes it feasible to estimate the inflow of groundwater to be about 42% of the total drainage water.