Tenochtitlan had a sophisticated system of urban planning with zoned public bathrooms (latrines, really) that were cleaned at night by a large labor force dedicated to keeping the city clean. The waste was collected by canoe from these bathrooms and dumped into the canal system where it decomposed and was later dredged up to fertilize and replenish the topsoil on the chinampas. Fresh drinking water was provided by mountain spring connected to the city by several aqueducts built in the 15th century.