In South Mediterranean conditions, during periods of severe drought mandatory watering restrictions can be established, such as the prohibition to irrigate crops. There is a need for growers of perennial crops such as A. donax to have data on crop response to dry conditions in order to decide on whether to keep or remove the crop. In this work, a four-year-old crop of nine A. donax ecotypes grown under optimal irrigation conditions was subjected to dry conditions for two years in a Xeric Mediterranean environment. Ecotypes performance in the two water conditions was assessed in order to provide data for growers to support their decision. Significant differences were found between ecotypes and water regimes for yield parameters. The interaction of water regime-ecotype was also significant, showing that the effect of the water regime change depended on the ecotype. The relative yield reduction of the mature crop ranged from 53% to 78%; this was as a result of the tough climate conditions in central Spain during the period of vegetative growth of A. donax. Over the whole experiment, an ecotype from South Greece outperformed and could be considered as a reference of the A. donax biomass potential in this environment. Further studies would be needed to assess the genetic distance among ecotypes, as well as to confirm the superiority of this ecotype in different environments.