Conservation tillage (CT) can be beneficial for soil, water and soil organic matter conservation in Mediterranean areas that are prone to soil erosion and where water availability for crops is the main factor for sustainability. CT is the best option to protect the soil from erosion, improve infiltration, reduce soil evaporation and so conserve rainwater to increase crop water use (WU) and also water use efficiency (WUE). While CT can play an important role in reaching the stability and sustainability of these agricultural systems, performance depends upon the choice and adoption of an appropriate soil management (tillage) system. In rainfed areas of the Ebro Valley, winter cereals are the main crop sown. This paper presents the results of 15 years of research in different soil and climatic conditions of the area of CT on water conservation, WU and WUE. Long-term experiments, comparing different tillage systems, were established in 1987, 1990 and 1992, at three locations in the Ebro Valley, chosen according to their degree of aridity (Selvanera, Agramunt and El Cano´s). Results reveal that CT was most effective in increasing yield under the driest conditions at Agramunt (10–15%), still effective with a smaller advantage under slightly wetter conditions at El Cano´s (5–10%) but ineffective at Selvanera, the wettest site. CT only increased WU in some years at Agramunt and never at the other two sites. The benefits of CT to both increased yield at Agramunt and El Cano´s were determined by improved WUE arising from changes in the pattern of WU before and after anthesis.