Groundwater is an important water source in urbanized areas. Cities across many geographies and climates, including Beijing, Mexico City, Buenos Aires, Los Angeles, Bangkok, Houston, Tokyo, Perth, and Lima, have all utilized groundwater to supply much of their potable water needs at some stage of development (Howard and Gelo 2002). Groundwater provides a significant portion of global urban water demand, though comprehensive statistics do not exist. Clarke, Lawrence, and Foster (1995) noted that half of all urban water use “has been attributed to well, spring, and borehole sources, and more than [1 billion] urban dwellers in Asia and 150 million in Latin America depend upon such sources.” Groundwater is prevalent throughout the urban hydrologic cycle, making it critical as a resource but vulnerable to pollution and over-exploitation.
Groundwater fulfills many supply-related functions. Young cities often tap groundwater to conveniently fuel rapid growth. Established cities, especially in arid areas, rely heavily on groundwater for potable use (Howard 1997). In many regions, groundwater augments available supplies during periods of drought and peak use. At the same time, groundwater overuse can lead to problems of subsidence, saltwater intrusion, growing pumping costs, and contamination of wells. Available water in an aquifer is governed by rates of extraction and recharge. While cities pump significant amounts of groundwater for supply needs, recharge is fueled by infiltration from precipitation and streams, as well as leaking pipes and irrigation runoff. Sewers and urban drainage reduce local urban recharge.
Groundwater has important roles for urban water supply. Groundwater often contains fewer contaminants than surface water through natural filtration of and protection from surface contaminants. As a limited resource, however, its role in an urban water supply portfolio tends to change over time (Morris et al. 1997, Howard and Gelo 2002). The intensive groundwater use during early stages of economic development benefits both urban and agricultural regions (Llamas and Custodio 2002).
While not all cities have plentiful nearby aquifer resources, cities that progress through eras of groundwater use, which are coordinated with different eras of development: 1) Exploitation, 2) Diversification, 3) Conservation, and 4) Conjunctive Use. Water use, measured as per capita water use, and the effects of groundwater use change across the four eras.
Conjunctive use represents a next era of groundwater management, where cities incorporate more advanced management of surface water, groundwater, and recycled water to maintain aquifer resources. Many innovative urban water management schemes include conjunctive use and coordinated management of surface water and groundwater resources. Conjunctive use requires an established and mature set of regulations that guide approaches based on hydrologic conditions and available water supplies. Large-scale conjunctive use at the watershed scale typically cuts across jurisdictions within a city or even between cities. Regional governance structures are required to collect runoff from large areas and move it to a select site that provides good infiltration. Cities face such regional management problems across many sectors of economic development, transportation, flood control, and water supplies. Yet, variability in climate and water supplies will spur many cities to increasingly use conjunctive use as a component of water management.
References
Clarke, R., Lawrence, A. & Foster, S.S.D. (1995). Groundwater: A Threatened Resource. UNEP Environ. Libr., 15.
Howard, K. (1997). Impacts of urban development on groundwater. In: Environ. Geol. Urban Areas (ed. Eyles, N.). Geological Association of Canada, St. John’s, Nfld., pp. 93–104.
Howard, K. & Gelo, K.K. (2002). Intensive groundwater use in urban areas: the case of megacities. In: Intensive Use Groundw. Chall. Oppor. CRC Press, p. 484.
Llamas, M.R. & Custodio, E. (2002). Intensive use of groundwater: a new situation which demands proactive action. In: Intensive Use Groundw. Chall. Oppor. CRC Press, p. 484.
Morris, B.L., Lawrence, A.R. & Foster, S.S.D. (1997). Sustainable groundwater management for fast-growing cities: Mission achievable or mission impossible? In: Groundw. Urban Environ. Vol. 1 Probl. Process. Manag. Proc. XXVII IAH Congr. Groundw. Urban Environ. (ed. Chilton, P.J.). Rotterdam, Balkema, pp. 55–66.