The value of irrigation efficiency cannot be precisely known. Therefore, water resources planning and irrigation network design are normally based on uncertain values of irrigation efficiency which ends up with disappointing results in practice. This research used "system" and "non system" approaches to analyze the data obtained from Pasha-Kola irrigation network in Mazandaran Province in northern Iran. This network is cultivated with rice and has a shallow water table condition. Furthermore, reported data for multiple cropping projects were obtained for Dez project in the Khuzestan province and Doroodzan project in the Fars province from other investigators and used to determine the "system" efficiency. In the "system" approach the deep percolation and surface runoff were not considered as water loss. However, these were considered as water losses in the "non system" approach. The project efficiency for "system" and "non system" approaches considering the deep percolation as water loss were obtained as 0.87 and 0.51, respectively. However, the project efficiency for the "non system" approach in which deep percolation was ignored was 0.85 which is similar to that obtained by the “system” approach. It may be concluded that, for irrigation projects with single crop (rice) and shallow water table, the project efficiency (either "system" or "non system") is generally higher than that of no shallow water multiple cropping networks. Furthermore, for rice irrigation projects, deep percolation of water may not be considered as loss due to its potential of being reused as groundwater supply and the "system" irrigation project efficiency is similar to the "non system" project efficiency. In general, it is more reliable that the "system" approach be used for evaluation of irrigation projects. Furthermore, in a "non system" approach the deep percolation may not be considered as water loss.