Adopting an historical-scientific approach, the following paper describes the methods developed during centuries for the measurement and distribution of water in the territory of Milan that, since the end of XII century, has covered one predominant role in Europe thanks to the development of advanced irrigation technologies, the construction of large canals (e.g. Naviglio Grande, Muzza) and creation of one capillary irrigation waterway network, as result of the initiative of local free institutions. This waterway network reveal technical elements from the engineering tradition of large aqueducts of ancient Rome, designed to reach a high number of final users that were in competition. A special focus is dedicated to the hydraulic writings of Leonardo da Vinci (late XV century), that uses the characteristic technical language of Milan engineers, with whom Leonardo collaborated, highlighting his tribute to the local hydraulic tradition. The long historical process, mainly based on empirical trials, finishes in the second half of the XVI century with the creation of the “Edifici Magistrali” by authorities of Milan. In advance of the Galilean scientific revolution, these special buildings allow to measure the water amount in a semi-precise way, transforming water like the other economic goods. This empirical model has maintained one leading position even after the birth of hydraulic science in 1628 (B. Castelli) and it has been admired and copied in many European countries until the mid of XIX century, as remarked in some French and English essays, devoted to Italian irrigation. The paper summarizes the reformist debate on the measurement and distribution of water amount started in Lombardy area at the time of the Enlightenment and continued during the Napoleonic Kingdom and the Restoration period.