In a context of severe water scarcity and high uncertainty of available irrigation water, the sustainable management of irrigation inputs to the crop has become necessary. The main objective of the present study was to determine the mid-term effect of water restrictions using different plant water status indicators of yield and quality of flat peaches. Three treatments tested were: (i) control (CTL), irrigated at ~100% of crop evapotranspiration (ETc) during the entire season; (ii) a regulated deficit irrigation treatment (RDI), irrigated as the CTL, except during the second fruit growth stage (~70% ETc) and late post-harvest (~50% ETc), with the same fertilization as CTL. During the first and second water deficit periods, an average weekly reduction of 43 and 109 m3 ha–1, respectively, allowed water savings of 33.6% in the RDI treatment with respect to well-watered trees. Irrigation water use efficiency increased by 45%, reaching values of around 4.16 kg m–3. Therefore, the optimization of irrigation water inputs in semi-arid conditions was achieved, by considering that the post-harvest period in this crop is a non-critical phenological period, with a stem water potential threshold value of around –1.4 MPa. Dynamic deficit irrigation protocols according to the water availability and stem water potential values were developed