Opportunities to enhance agricultural productivity in arid Tunisia have been the domain of active investigation during the last years. Many field experiments were carried out on the potential of using limited amounts of saline water from wells to grow profitably crops. This paper concerns the performance of the potato crop grown in commercial farms under relatively stressful conditions. The FAO-Water Balance calculation method was applied for irrigation scheduling over three contrasting seasons. Results obtained from full and deficit irrigation treatments show that under optimum irrigation, marketable yields varied from about 40 t/ha to 20 t/ha , and water productivity from 11.7 to 9.1 Kg/m3, respectively for the spring and autumn periods of the year. We propose here a simple linear relationships between yield (Y, t/ha) and total water application (Q, mm) to be used for quick appraisals of attainable yields of the potato crop when waters of about 3-3.5 dS/m are used. Within a range of 150 to 350 mm total water supply after planting the models are [Y