Integrating current and historical water chemistry data with long-term piezometric records to develop a regional-scale conceptual flow model: Las Salinas spring, Medina del Campo, Spain

•An original research on the origin of salinity in a multilayer aquifer is presented.•Some geological aspects present enough relevance to support a conceptual model.•Hydrogeological data, sedimentary records and hydrochemistry are the key of changes.•Results are useful for achieving a sustainable aquifer management.