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.

Securing water supply is an extremely important issue following an earthquake. Recent earthquakes in Japan have prompted focus on the use of groundwater or disaster emergency wells (DEWs). Water supply networks are vulnerable to earthquakes because they comprise long-distance pipelines that are not always earthquake-resistant. Groundwater, however, can usually be found directly below an area where water is required and can serve as an alternative water source. Although previous studies discussed the importance of groundwater in relation to natural disasters, with special reference to drought, little attention has been given to the use of groundwater following earthquakes. In this study, two questionnaire surveys were conducted of DEW owners and welfare facilities for elderly people in Kumamoto (Japan), which was struck by an Mw 7.3 earthquake in 2016, to identify the advantages and disadvantages of using groundwater as an emergency water supply and ascertain policy issues to be resolved for making DEWs effective. Results showed that not only 30 DEWs but also at least 25 privately owned wells not registered as DEWs were open to the public in the early restoration stage, improving people’s access to water and decreasing the burden on the Kumamoto city government’s emergency water supply. However, it was revealed that groundwater might not always be potable owing to quality concerns. Additionally, only a limited number of welfare facilities used the available adjacent DEWs and DEW recognition level remains low. These findings indicate that improving information disclosure regarding emergency groundwater use is a policy issue to be resolved.

Concern has grown regarding how public and private sectors should make effective use of local groundwater to alleviate negative impacts of water-supply cutoff following an earthquake event, which can be regarded as an emergency groundwater governance problem. Existing literature on groundwater governance, however, is based on the tacit assumption of groundwater utilization under normal social conditions, and scant consideration has been given to the role of groundwater following occurrence of a natural disaster. This study conducted questionnaire surveys to reveal how groundwater was used in three cities (Kumamoto, Sapporo, and Sendai) in Japan struck by large earthquakes between 2010 and 2020. Results revealed substantial differences between these cities in terms of groundwater utilization following earthquake occurrence. The time between the restoration of the electricity supply and restoration of the waterworks, and the social capital accumulated by local governments, are indicated as possible reasons for such differences. Analysis also identified policy challenges for improved groundwater governance in an emergency: (1) establishment of a strategy for emergency water supply through combined use of groundwater and other water sources, (2) enhancement of methods for timely inspection of groundwater quality following occurrence of a disaster, (3) maintenance of records of the number of registered disaster emergency wells (DEWs), (4) creation of methods for publicizing locational information on DEWs with adequate regard for the privacy of well owners, and (5) recognition of the importance of making DEWs part of overall disaster preparedness.