In the arid west, increased irrigation efficiency is one of the most commonly suggested solutions to our water problems. But Jay Lund and Thomas Harter point out the dilemma:

In many areas, drought-year groundwater supplies depend substantially on irrigation inefficiency in wetter years, when surface water is available and used by farmers. Ironically, local inefficiency often improves regional water use efficiency and sustainability. However, excessive groundwater pumping causes long-term continual decline in groundwater levels (“overdraft”) and irrigation inefficiency increases salt and nitrate loads to groundwater. There are few perfect solutions in water.

Mixed bag.