If a crop does not get enough water to meet its maximum demand, yield will decline. In fact, crop yield increases as water availability increases to the level of peak crop water use. More irrigation beyond this level does the crop no good, and may actually cause harm. Increased pumping and water costs erode profits. Excess irrigation water may run off or percolate below the root zone, removing nutrients and chemicals from where they are needed.
Crops use water for several purposes.
During hot periods, the most important use is to cool the plant. In the same way, water that evaporates from a plant cools the plant. Without evaporative cooling, the sun's energy would quickly overheat plant leaves. Cooling is such an important function that plants evaporate more than 99 percent of the water they absorb during their lifetime. A second function of water is to transport nutrients throughout the plant.