“Caja del Auga” translates loosely as “The Water Box” but it’s really a very fancy cistern, once used to keep the city in water and the fountains flowing. It’s become one of the symbols of San Luis Potosi. Here’s a translation from the SLP information webpage:
“The Water Box is a circular structure of neoclassical style, made of quarry rock, with ornamental masonry, a pyramidal tile roof and a finial in the shape of a pineapple. This container received water that came from the spring of the Cañada del Lobo in the Sierra de San Miguelito (discovered in 1617 at the time of the Viceroyalty), by means of a long aqueduct with some intermediate sources.
The city grew and this spring was a salvation bringing the water to the inhabitants of the capital city. The Aguador was in charge of supplying the families that did not have the precious liquid in their houses.
The first governor, Ildefonso Diaz de Leon initiated the great hydraulic project in 1828. The author of the design is the engraver and painter José Guerrero Solachi and the executor Juan N. Sanabria; It was installed on Calzada de Guadalupe and put into service in August of 1835.
This monument is the pride of potosinos and, because of its beauty and permanence, is the symbol of the city. It is in such a good state that when it rains a lot, water is still stored in it.“