In the Punic age, the water supply was ensured only by the presence of tanks for water storage and a few wells, while in the Roman Imperial age, a very effective aqueduct system for transporting water was built to serve the needs of the people of Tharros, especially to provide water for the baths (thermae).
Traces of the aqueduct are still visible along the road that leads to the Tharros archaeological area and down the slope to the wide beach. Its walls were built in layers by alternating blocks of sandstone with bricks.
It was assumed that the aqueduct was just over 500 meters long and transported water into the city from a well located outside the city. The Porta Cornensis, an arched door that was discovered in a collapsed state on the beach near the shoreline, was probably part of the aqueduct. It is assumed that the aqueduct supplied water to the castellum aquae, an almost square structure that was located in the center of the city, between the cardo maximus and the decumanus. The castellum aquae served as the reservoir for water transported via the aqueduct system to Tharros. The external sides of the castellum aquae were built with two rows of sandstone blocks alternating with two rows of bricks often referred to as opus vittatum mixtum. The interior was made entirely of brick.

The internal space of the castellum aquae is divided into three corridors by eight pillars that originally supported the roof. Only a small part of the roof was preserved. The outside walls were covered with white plaster, while the inside walls were covered with a thick layer of earthenware, which served as waterproofing.
A rectangular space that was discovered adjacent to the southern wall was assumed to be a settling basin.

Adjacent to this space was a semi-circular base of sandstone blocks, with a floor made of bricks and plumbing plaster, which was considered to the structural part of a fountain.