Excessive groundwater pumping is now a global concern. There is no panacea for this problem, which needs to be addressed through continual policy improvements based on case studies. Good examples of the diversity of groundwater management are demonstrated by the Tokyo (Japan) and Orange County Water District (OCWD, California, USA) experiences. In Tokyo, excessive groundwater pumping was addressed through technological restrictions, including restrictions on the diameter and depth of wells, and construction of industrial waterworks. On the other hand, in Orange County, OCWD introduced a pump tax to purchase external water for artificial groundwater recharge. These two strategies are in striking contrast, from two perspectives. First, while OCWD's main policy tools were tax and artificial recharge, Tokyo depended on technological restrictions and construction of waterworks. Second, OCWD uses a combination of surface water and groundwater, but water supply in Tokyo has shifted almost completely from groundwater to surface water. What are the strong and weak points of each strategy? What causes such diversity? In this paper, a comparative case study was conducted to clarify (1) the institutional contexts causing the diversity of groundwater management and (2) the advantages and disadvantages of each policy combination.

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