Scarce water resources management makes accurate measurements of different parameters of water requirements very critical. Therefore, the values for crop evapotranspiration and crop water requirement are identical. Crop water requirements refer to the amount of water that is needed to be supplied efficiently. Therefore, there are many models and tools which were used in this study are used in this study as a practical tool to calculate actual evapotranspiration such as the CROPWAT model. Moreover, Eddy Covariance and ET-Watch model are methods used to estimate evapotranspiration. The main goal of the study was to assess daily and decadal actual evapotranspiration using Eddy covariance and ET-Watch model under arid land conditions then compare results with CROPWAT model result. Egypt was used as an example. Results showed that Eddy covariance ETa values for both crops were lower than ETa values from CROPWAT, while ET-Watch values were somewhat close to CROPWAT values.  For cotton, the intercept of the linear relationship for daily ETa were 1.737 and 2.15, respectively between Eddy covariance and CROPWAT. For decadal ETa were 1.91, 2.039 ETWatch and CROPWAT.  While for wheat crop, the intercept of the linear relationship for daily ETa were 1.09 and 0.663, respectively between Eddy covariance and CROPWAT, ETWatch and CROPWAT. For decadal ETa were 1.101 and 0.69. Its highly recommended to use ETWatch when predicting daily ETa, while for decadal ETa both Eddy covariance and ETWatch could be used with no big differences.