This study analyzes the potential for water savings from irrigation efficiency improvements in California, USA. We model water savings associated with three efficiency scenarios in wet, average and dry water years. The ‘efficient irrigation technology’ scenario shifts a fraction of the crops from flood irrigation to sprinkler and drip systems; the ‘improved irrigation scheduling’ scenario uses local climate and soil information to more precisely meet crop water needs; and the ‘regulated deficit irrigation’ applies less water to crops during drought-tolerant growth stages to save water and improve crop quality or yield. The three scenarios evaluated here each conservatively show the potential for significant water savings. Their combined potential applied water savings are between 5.6 × 109 m3 (4.5 million acre-feet (MAF)) in a wet year and 7.4 × 109 m3 (6.0 MAF) in a dry year. In total, these scenarios could reduce water applied to California agriculture by 17% or reduce water consumed by California agriculture by 13%. The results also indicate that water conservation and efficiency improvements are particularly effective in dry years, when agricultural water demand is greater and conflicts over scarce water resources are more severe. These approaches can reduce vulnerability to increasingly uncertain water supplies.