WATER P-NOTES ISSUE 18 OCTOBER 2008 46470 Groundwater in Urban Development: Assessing Management Needs & Formulating Policy Strategies P eople have clustered at the water's edge although sometimes with a substantial time lag. But throughout civilization for the most fundamen- those favorable conditions are severely altered when tal of reasons: without water there is no life. the ground above is overbuilt. Every major city in the world has a body of water or aquifer nearby, since although rivers and lakes pre- determined where people would gather and dwell, The threat of urban groundwater groundwater constitutes about 98 percent of the degradation fresh water on our planet (excepting that captured in the polar ice caps). This makes it fundamentally That major cities affect the aquifers they overlie can important to human life and to all economic activity. be taken for granted, since water supply, sanitation, Groundwater resources in and around the ur- and drainage are inextricably linked with ground- ban centers of the developing world are exception- water and are an essential part of the urbanization ally important as a source of relatively low-cost and process (figure 1). That urbanization should change generally high-quality municipal and domestic water an aquifer for the worse, however, need not be in- supply. At the same time, the subsurface has come to evitable. The key to avoiding this is not to lose sight serve as the receptor for much urban and industrial of the subsurface environment when planning the wastewater and for solid waste disposal. There are urban water infrastructure. increasingly widespread indications of degradation in Individual waterwell diggers and municipal the quality and quantity of groundwater, either serious authorities like good groundwater for the same rea- or incipient, caused by excessive exploitation and/or sons: it is cheap, clean, and reliable--at least at the inadequate pollution control. The scale and degree initial stages of urbanization. So pumping ground- of degradation varies significantly with the susceptibil- water makes good sense. But over time the rate ity of local aquifers to exploitation-related deteriora- of exploitation (or groundwater abstraction) must tion and their vulnerability to pollution. Management be adjusted to the replenishment (or groundwater strategies need to recognize and to address the com- recharge) rate. The ability of society to adjust and plex linkages that exist between groundwater supplies, adapt, therefore, becomes the critical factor. Cities urban land use, and effluent disposal. and their surrounding jurisdictions must make the Groundwater tables have become the focus right decisions on infrastructure development, for of keen interest in recent years, as the supplies of example ensuring that industrial effluents and solid water underlying urban areas have dwindled and waste are handled in ways that do not threaten the deteriorated, threatening the millions of people aquifer on which the city is built. who live above. When conditions are right, aquifers Water sustains urban life and the soil has to refill regularly from infiltrating rainfall and runoff, absorb much of it after use. Whether, how quickly, Excerpted from Water in Urban Development: Assessing Management Needs and Formulating Policy Strat- egies Ground by Stephen Foster, Adrian Lawrence, and Brian Morris (World Bank Technical Paper 390, March 1998)--a GW-MATE publication. Visit www.worldbank.org/gwmate/ for more information. The publication is available for download in PDF format from www.worldbank.org/water. WATER P-NOTES Figure 1. Interaction of groundwater supply and wastewater disposal in a city overlying a shallow aquifer Water Supply Wastewater Surface Disposal Re-use Water Pluvial Sewage Drainage (Piped) Use ±Treatment Peri-urban Urban On-site Sanitation and Irrigation Wellfields Wells Industrial Effluent Disposal (Excess Flows) Groundwater Abstraction Aquifer and in what state that water returns to aquifers is Groundwater over-pumping a question urban planners and managers must may lead to a sinking city address. Heavy rains and prolonged droughts are obvious variables that affect groundwater levels-- Mexico City, one of the world's largest, serves as but they are not the only ones. a dire warning of what can happen when ground- During the early stages of urbanization, a suit- water is over-pumped (figure 2). From before the able subsoil can be the best natural receptor for Spanish conquest Mexico depended upon ground- wastewater and on-site sanitation is the preferred water to slake its enormous thirst. But from the solution that need not necessarily impact adversely 1950s onwards with escalating population and on groundwater quality at depth, but in unfavour- mushrooming water demand, groundwater abstrac- able conditions other arrangements must be made. tion increased rapidly, even with supplementary Where the subsoil shows adequate filtration capac- water-supplies brought in from afar. ity, the ground will also be the most appropriate receptor of urban runoff, so as to avoid or reduce the need for costly surface drainage systems. But as cities grow, and building and population density Figure 2. Population growth and increase then on-site solutions may no longer be water demand in Mexico City feasible or appropriate. 25 100 But sewage and/or industrial effluents, if al- 20 80 /s) lowed to percolate into the ground above vulner- 3 (m able aquifers in excessive amounts, can cause (miilions) 15 60 serious problems and ruin what had been a source 10 40 Supply of clear, clean water. Lack of responsible environ- 5 20 mental management can thus make the precious opulationP aterW groundwater resource unsafe for consumption. In 0 10 coastal areas in particular, aquifer degradation by 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 salinity poses an equally serious threat if groundwa- Year ter abstraction is not regulated and over-pumping is Population Imported water Local groundwater allowed to occur. Source: Mazari and Makay, 1993. 2 ISSUE 18 · OCTOBER 2008 Mexico sits astride an aquifer whose groundwater most sprawling cities, population growth precedes was depleted to such an extent that compaction of construction of mains sewerage and wastewater the soft ground in sections of the historic city occurred treatment facilities--and in the meantime shallow and the land surface has sunk 8 meters or more over groundwater can become contaminated from in-situ the last 60 years. A professor at Mexico's National sanitation. It may be years before the full extent of Autonomous University brought this phenomenon to pollution becomes apparent, because contamination the world's attention more than a decade ago when of large aquifers is a gradual and hidden process. he pointed to a waterwell casing protruding high into And full remediation of entrenched problems may be the air near the National Revolution Monument, the prohibitively expensive, even for high-value public top of this `pipe' having been at ground level when water supply use--thus it is critically important to rec- the monument was built in 1934. ognize the incipient signs of groundwater pollution. Knowledge of the danger of groundwater pol- Managing groundwater for lution and fundamentals of groundwater protection future use are now widely accessible, putting the onus on en- vironmental managers both to think ahead and to respond coherently. There is no time to waste. Half The principal aim of this publication is to draw the world's population already live in urban areas, attention to the need always to integrate consider- and the need to shield aquifers from pollution and ation of groundwater, when making decisions on depletion is self-evident. urban infrastructure planning and investment. This is not as simple as it might first appear, and even Municipal, provincial and national govern- with well qualified people at hand, there needs to ments (supported by international institutions) must be keen awareness of the importance of building a find the political will, and the practical means, to network of specialists to ensure sound evaluations. control groundwater demand, to limit groundwater abstraction by socio-economic and/or regulatory People and institutions concerned with urban measures,, to provide alternative water supplies water supply and environmental management often where necessary, and to handle and treat sewage have a poor understanding of groundwater. And in and industrial effluents adequately (table 1). To be Table 1. Urban groundwater supply management: objectives, problems, and mitigation measures Objectives Problems Targets Mitigation measures Maintain Decline in well Constrain Redistribute or reduce abstraction (e.g., by groundwater yields due to groundwater reducing water-main leakage) supplies falling water table levels Increase urban recharge Safeguard Unacceptable Moderate Restrict contaminant loading from identified sources groundwater quality of subsurface Restrict residential development in vulnerable areas quality drinking water contaminant load Control industrial effluents Zone land for different uses Control landfill location and design Separate waste disposal from groundwater supply Increasing salinity due Constrain Redistribute or reduce abstraction to sea water intrusion groundwater Modify depths of water supply boreholes levels Contaminants brought Constrain Increase abstraction of shallow polluted in from contaminated groundwater groundwater for nonsensitive uses land by rising water table levels Reduce urban recharge 3 WATER P-NOTES effective all such measures need to be based upon coordinated. An absolute requirement for the prac- a sound hydrogeological framework. tical definition and implementation of groundwater Even after a regulatory agency has defined a management policies is to set priorities systemati- rational policy for groundwater management, chal- cally and clearly. lenges remain. No matter how rational such policies An essential need for public and stakeholder appear to be, they may not be considered politi- communication is a clear explanation of the con- cally attractive or acceptable, especially in the case sequences of `non-intervention'. Groundwater is of groundwater, which is "out of public sight," and often degraded because of a lack of knowledge therefore "out of political mind." Moreover, power- of the aquifer system, coupled with uncontrolled ful groups can interfere with the regulatory process. groundwater abstraction and urban wastewater dis- In finding a way forward, the environmental posal. Little consideration is given to the costs that regulatory agency needs to build social consensus may be incurred either to reverse the deterioration to overcome resistance to the introduction of sci- or to replace the lost asset. The marginal cost of entifically and economically logical policies, and replacement water supply sources is invariably high; use its regulatory powers effectively. A key factor and action to reverse degradation, especially when is the formation of well-informed water user inter- it is advanced, is generally a long term and costly est groups along with more general groups of process. The stakes are high. Unless groundwater groundwater stakeholders. Such groups can act as is protected, in terms of quality and quantity, it will vehicles for policy implementation and operational become scarce, expensive, and hazardous to hu- management at the practical level when adequately man health. The Water Sector Board Practitioner Notes (P-Notes) series is published by the Water Sector Board of the Sustainable Development Network of the World Bank Group. P-Notes are available online at www.worldbank.org/water. P-Notes are a synopsis of larger World Bank documents in the water sector. 4 THE WORLD BANK | 1818 H Street, NW | Washington, DC 20433 www.worldbank.org/water | whelpdesk@worldbank.org