In intensive irrigated farming systems, the way to improve productive efficiency depends on the proper management of resources. With the implementation of the Alqueva global irrigation system in the southern Portugal region of Alentejo, agricultural intensification is a reality that imposes to farmers the challenge of producing more and more efficiently, ensuring the farming systems sustainability. This work resulted from an on-farm demonstration project carried out in two locations in the Alqueva region. Water use and water productivity were studied during 2012/2013 and 2013/2014, in three double cropping systems: a maize monoculture (MM) and two rotations, barley + maize-barley (BM-B) and sunflower-barley + maize (S-BM). Maize yields were influenced by the length of the crop cycle. In the rotation BM-B, with a predominance of autumn-winter crops, water requirements were lower and the total volume of irrigation applied was approximately half of the monoculture (5930 m3/ha and 13,230 m3/ha, respectively). When the potential crop yield was reached, maize had the higher water productivity (the highest value achieved was of 2.7 kg/m3). Overall, as a result of the lower yields achieved, the water productivity values indicate a less balanced performance of the S-BM rotation.