The diagram shows the construction system of the rainwater collection tanks. The cistern was built in an excavation of at least three meters in diameter for a depth of 5 to 10 meters. At the base there was a platform with “rudders” in lava stone. The side walls, made of light lava stones, and the base were made impermeable with the “beaten lapillus”. Rainwater from the solar paving blocks led into the cistern through terracotta canals called “curzi”. The construction of a cistern also required a year’s work. The recovery of rainwater was essential for domestic and agricultural uses as it was cheaper than the construction of wells.