Evaluating groundwater recharge is crucial to assess available water resources, to establish environmental flows when aquifers are connected to surface water or wetlands, and to anticipate fresh/saline water interface dynamics. In intensively irrigated areas, where close to field capacity conditions are maintained, rainfall events usually fully turn into recharge. Separating the respective contribution of recharge from rainfall and irrigation return flow is therefore a hard task. Nonetheless, exceptional storms provide unique opportunities to better constrain the instantaneous response of aquifers and provide valuable data that would have been hardly obtained elsehow. In December 2016, an extraordinary storm with up to 286 mm of rainfall in 60 hours induced severe flooding in certain areas of Campo de Cartagena. Exceptional groundwater recharge was traduced into increased submarine groundwater discharge and locally by saline extrusion to the coastal Mar Menor lagoon, itself in a critical state due to eutrophication processes. Potentiometric measurements realized before and after the storm, together with data from lysimeters and automatic sensors for water head, EC and temperature provide interesting inputs on the functioning of the aquifer and its impact on the Mar Menor lagoon.