The work consists in the creation of safety areas, by means of the chronological method, of wells for drinking water in the city of Prato (Tuscany, Italy). The aquifer of Prato plays a fundamental role in supplying water to the municipality as it is the principal source. The area comprises the alluvial fan of the Bisenzio River, right hand affluent of the Arno River, at the meeting point with the fluvio-lacustrine plain of the intermediate Valdarno valley, between Pistoia and Firenze. The strong groundwater demand for both public and industrial purposes has caused the progressive lowering of the water table in recent years. Given the importance of this resource this work aims to protect the city’s water supply. In particular, the objective is to use mathematical modelling to analyse the groundwater dynamics, in order to identify the areas of recharge, localise and classify centers of pollution and study their possible interferences. The software Modflow is used to construct the isochrones of the more productive wells with the chronological method. The results also demonstrate that protective buffers created with the geometric criteria (circle with a 200 m radius) tend to underestimate the size of the safety areas and, therefore, to reduce the protection of the wells