For example, producing almonds is highly profitable when water is cheap but almond trees are thirsty, and almond production uses about 10% of California's total water supply. The thing is, nuts use a whole lot of water: it takes about a gallon of water to grow one almond, and nearly five gallons to produce a walnut. "Suppose an almond farmer could sell real water to any buyer, regardless of county boundaries, at market prices—many hundreds of dollars per acre-foot—if he agreed to cut his usage in half, say, by drawing only two acre-feet, instead of four, from his wells," say the authors. "He might have to curtail all or part of his almond orchard and grow more water-efficient crops. But he also might make enough money selling his water to make that decision worthwhile." Using a similar strategy across its agricultural industry, California might be able to reverse the economic logic that has driven farmers to plant more water-intensive crops. "This would take creative thinking, something California is known for, and trust in the power of free markets," conclude the authors adding that "almost anything would be better, and fairer, than the current contradictory and self-defeating regulations."