The project aimed to investigate water supply in ancient Pompeii and in particular to identify the sources which fed the aqueduct of the Roman city in the imperial period. Thus, samples of limestone residue were collected and analysed from the Castellum Acquae, the “overflow” towers, from the cistern of the Stabian Baths, from the pool in Villa A at Oplontis (modern Torre Annunziata, NA) and from the remains of the aqueducts situated in the territory of Palma Campania (NA) and Sarno (SA). The results established that the sources used were the same for the aqueducts of Pompeii, Palma Campania and Sarno and that in the city’s last years the sources used were different to those used when the aqueducts first began to function.