The theme of the knowledge of the Milanese engineers and of Leonardo da Vinci is dealt with by examining two projects : one connected with the establishment of a model of the water outlets of the Naviglio Grande, in order to control their rate of flow ; the other with the building of a canal on the side of the Adda. The relation of some drawings of water jets by Leonardo with the mathematical and philosophical dimension of his thoughts on the motion of water is also discussed.