This is the most important construction in the uninhabited village of Mazmúllar. It is an imposing cistern distributed in 9 compartments separated by horseshoe arches, with impermeable walls of reddish clay. It has a capacity of 120,000 litres. On the top of one of the arches is engraved in rudimentary Arabic script the shahada or profession of Islamic faith (La ilaha illa-llah Muhammadun rasulu-llah - There is no God but Allah. Muhammad is his Messenger).