In Tunisia, the development of the irrigation within the water scarcity context, remains one of the crucial issues of agricultural activity. The phenomenon of climate change is likely to make the problematic while threatening the country's food security. Thus, water use efficiency is essential to overcome these constraints and to preserve productive and sustainable agricultural activity. This work aims to optimize the water irrigation use and to increase the production of the durum wheat (DW) through improving irrigation practices. For this, a field survey was carried out with a sample of 43 farms from the Siliana region. In order to collect the required data, we have focused on the DW activity during the agricultural compain of 2015 in terms of the applied doses of water and fertilisers as well as the crop rotation. . Using CROPSYST, a crop model has been developed. The model was calibrated and validated to replicate the DW activity during three consecutive crop years 2015, 2016 and 2017. Three strategies of varied mix in terms water irrigation and fertilizers doses were simulated, The results showed the improvement of the yield by 9% that allowed an improvement of the water productivity up to 8.2 kgha-1mm-1. Given these results the Gross Margin may increase by 3% up to 11%.