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Estimation of groundwater recharge in a semi-arid area is difficult due to the low amount and variability of recharge. In the El Haouaria region (N.E. Tunisia), this hydrodynamic survey revealed a decrease in unconfined groundwater reserves of approximately 11% over the last 30 years due to the abstraction of water. Over that same time period, the groundwater table displayed a natural decrease of about 10 m in depth over an area of 230 km(2). Hydrogeological investigations have shown that two aquifers which vertically integrate all of the permeable zones in the region can be distinguished: a shallow aquifer formed by filling the Quaternary and another deeper one in the Pliocene. These two aquifers are separated by a semi-permeable layer through which vertical exchange by seepage is possible. Two analytical models, taking into account the long term decrease of the water table, were used to interpret H-3 and C-14 content in groundwater. Forty groundwater wells were sampled to obtain additional information on isotopic characteristics of the groundwater defined in previous studies. The median annual renewal rate (recharge as a fraction of saturated aquifer volume) varies between 0.2 and 0.3 %. For representative characteristics of the aquifer (30 m of saturated thickness, porosity 14%) this implies a recharge of 10 to 12 mm/yr. Which is lower than estimates of 18 to 36 mm/y obtained using hydrodynamic methods. (C) 2015 Published by Elsevier B.V.