Groundwater withdrawals in the United States and globally expanded dramatically during the last half of the 20th century. Estimates of groundwater withdrawals in the United States are available from the United States Geological Survey for every five-year period since the 1940s. These data (Figure 1) show a steady growth through the 1970s, followed by a more or less stabilization of groundwater use. In 2015, total groundwater withdrawals were about 114 km3/yr (82,300 million gallons per day [MGD]), and 69 percent of the groundwater withdrawals was used for irrigation and 18 percent was used for public supply (data from Dieter et al. 2018). Approximately half the population of the world depends upon groundwater for its drinking water supply, and groundwater supplies about 43 percent of the global irrigation water supply (Siebert et al., 2010; WWAP, 2015). Total global groundwater use in 2010 was approximately 982 km3/yr, and about 70 percent of that was used for irrigation (Margat and van der Gun, 2013). As of 2010, the country with the largest groundwater use was India (about 250 km3/yr) more than the second and third largest users combined (China and the United States, with about 110 km3/yr each). This large and expanding use of groundwater is the primary driving force for concerns about groundwater depletion and sustainability of groundwater pumping.