The Cervialto massif hosts one of the main karst aquifers of the southern Apennine (Italy). This aquifer feeds the Caposele spring, a basal spring characterized by a strongly delayed and damped response to rainfall (and snowmelt). Contrary to typical karst springs, no discharge peaks following rainfall are observable in the daily hydrograph, which shows a smooth seasonal fluctuation during  normal-wet years and is almost flat during droughts. This study focuses on the modeling of the recharge-discharge process of the Cervialto aquifer by a lumped reservoir model. The KarstMod modeling platform was employed to transform the daily affluxes into spring discharge. The study investigated the ability of a lumped reservoir model in predicting the daily discharge of a diffuse-flow karst system, which has been little discussed in the literature.