From Water Supply Crises to Building Urban Water Security

Secure, affordable, and equitably delivered high-quality water supplies are central to human health, well-being, and economic development—especially in urban areas. Despite efforts by many policymakers to invest in healthy ecosystems and responsible management practices, a quarter of the world’s 500 largest cities already experience water stress, affecting nearly 400 million people and $4.8 trillion in economic activity.

Because of varied combinations of climate change, population growth, overextraction of natural resources, and pollution, cities around the world have had to navigate severe water supply crises. Many cities have been to the brink—they have had to confront near-catastrophic risks to their water supplies.

Challenges and Constraints

Making decisions to secure water supplies during a crisis is a poor way to design robust and resilient systems, and cities at the brink are not well-positioned to invest the time and resources needed to prioritize justice and equity. Cities, and the millions of people who live in them, would be much better served by proactive, collaborative, and holistic planning and investment ahead of a crisis—that is, building urban water security.

But policymakers face a variety of challenges and constraints when developing plans for urban water security, such as

• navigating financial, political, environmental, and administrative contexts
• accounting for cascading effects and linked systems
• identifying solutions that reinforce collective rights and security rather than entrench hierarchies and barriers.

Building Urban Water Security

We examined recent urban water supply crises around the world to identify lessons learned and offer a framework for evaluating cities’ available pathways for building water security. Although dozens of global cities have had to confront a severe water supply crisis, we focused on Cape Town in South Africa, São Paulo in Brazil, Melbourne in Australia, and Las Vegas and New Orleans in the United States. More information on the study, data collection, and our analytical approach can be found in our full report.

Using interviews with experts and policymakers, and after closely reviewing policy reports and academic analyses, we identified five ways cities can act now to build urban water security in the future:

• invest and plan ahead of a crisis
• build capacity to take a systems-level approach
• strengthen collaboration between governments
• embrace innovation
• build trust and communication.

Mobilizing the resources and expertise needed to make these shifts will require strong local leadership, public engagement, and intergovernmental support.

Cape Town

Nature of the Crisis

Cape Town, South Africa, relies on a series of six reservoirs for 95 percent of the city’s water supply, which supports just over 4 million people, with 14 percent living in informal housing. Three years of severe drought, from 2015 to 2018, caused the reservoirs to drop from 100-percent capacity in 2014 to as low as 38 percent. The city had successfully navigated prior droughts but had not planned for such severe conditions.

Poor infrastructure maintenance, delayed capital investments, inadequate tariff structures, intergovernmental coordination challenges, and population growth contributed to the severe water shortage.

Response

Cape Town responded with a combination of residential and agricultural water-use restrictions (including the use of household flow regulators), infrastructure improvements, supply augmentation, increased water tariffs, and public-awareness campaigns.

The city launched a water dashboard on its website to display weekly updates on dam levels and water use. This was supplemented with regular updates on what the city was doing to manage the system and household-scale maps of residential water use. As the drought worsened, these efforts culminated in the publicization of Day Zero in November 2017, or the point at which water would be turned off in neighborhoods and residents would need to fetch a daily allocation of water at public points of distribution.

Status

Conservation efforts resulted in a 50-percent reduction in citywide water consumption. In spring and summer 2018, strong rainfall led to city officials canceling Day Zero and, by the end of the winter, the reservoirs were above 75-percent capacity. Per capita water use has rebounded but not entirely.

The city continues to monitor and publicize water use and management efforts and is making needed infrastructure upgrades. Challenges remain, however, related to intergovernmental communication and coordination, along with trust-building between the city and its low-income neighborhoods.

Key Insights

• Experiences and access vary by income level: Many Cape Town residents with low incomes lacked reliable water supplies prior to the Day Zero water crisis, and their experiences were often very different from those of middle- and high-income residents. The city’s responses to the drought, including introducing charges for basic water use, were criticized for their disparate effects on poor and wealthy neighborhoods.
• Inequities are not always apparent in the data: Residents in higher-income neighborhoods could often afford to dig their own private wells to avoid restrictions and increasing tariffs while many low-income households lost water access because of the city’s reduction of pressure in the system to conserve water and the inability to pay the higher water rates. Thus, metrics that center on average per capita water consumption can mask inequity.

Cape Town officials have heeded many of these lessons and are working to incorporate more voices in its water-use planning.

New Orleans

Nature of the Crisis

In 2023, a drought in the midwestern United States caused lower-than-average water levels in the Mississippi River, which the city of New Orleans, Louisiana, relies on for 100 percent of its drinking water. The relatively low flow downstream allowed for the upstream movement of saltwater from the Gulf of Mexico because of the elevation difference in the two water sources, which is exacerbated by long-term dredging for maritime transport.

This saltwater wedge presented a looming water supply crisis for the city because its aging drinking-water system, including a drinking-water treatment facility last renovated in 1959, was not equipped for the increased salinity.

Response

To stave off the saltwater wedge, the U.S. Army Corps of Engineers (USACE) built a sill, or an underwater barrier made of sand on the bottom of the Mississippi River. However, the sill height was too low, so saltwater topped the sill in July 2023 and was anticipated to reach New Orleans by late October.

State emergency managers and members of the Federal Emergency Management Agency, the Sewerage and Water Board of New Orleans (SWBNO), and USACE very quickly coordinated to mitigate the looming disaster. The group had approximately four to five weeks before the anticipated saltwater wedge would reach the New Orleans’s drinking-water intakes. Options to avert the crisis included barging in freshwater, building pipelines, and constructing a cofferdam (a three-sided barrier) around the drinking-water intakes. Ultimately, though, none of the options were used. SWBNO released information on the salinity of the water intakes because of public concern that not enough actions were being taken to protect the city’s drinking water.

Status

Droughts in the greater Mississippi River watersheds have caused saltwater wedges before 2023 and climate change will likely cause more drought events, leading to more saltwater wedges in the future.

Because of limited resources, it is difficult for the city of New Orleans to undertake any large-scale infrastructure projects or update its drinking-water system to prepare for the next intrusion event. However, SWBNO learned that early, honest, and frequent communication about the water quality’s status is important for building and maintaining public trust.

Key Insights

• Collaboration is key: The numerous decisionmakers who would be involved in a New Orleans water crisis need to collaborate to slow saltwater intrusion events and treat affected drinking water. Both USACE and SWBNO are working to help mitigate saltwater intrusion events and are collaborating on the monitoring and reporting of salinity levels.
• Multiple uses of water sources require managing: USACE must manage the trade-offs of the Mississippi River’s multiple uses and the effects of these uses. USACE has a duty to maintain the Mississippi River and manage maritime transport, which involves dredging the river periodically. Although dredging the river exacerbates saltwater intrusion events during droughts, USACE builds sills to slow or stop the saltwater wedges. Additionally, USACE brings freshwater to the affected drinking-water intakes via barge.
• Transparency and communication are necessary to build public trust: SWBNO already combats flooding events, aging infrastructure, and lead pipes. Public trust in SWBNO is low, especially following the 2023 saltwater wedge event. Since then, the Louisiana governor created a task force to determine whether SWBNO needs a different governing structure. Despite this, a long-term lack of trust from the community will hinder New Orleans’s efforts to make needed investments to prevent a saltwater wedge crisis in the future.

Response

In place of outright rationing, the Basic Sanitation Company of the State of São Paulo (Saneamento Básico do Estado de São Paulo, or SABESP) implemented three major response measures:

• pressure reductions to reduce overall water use
• fiscal incentives, including discounts in water pricing for below-average water use and surcharges in water pricing for above-average water use
• community outreach campaigns to help reduce water use.

Although the measures were somewhat successful in reducing demand, they amplified inequities across the region because lower-income communities were disproportionately affected by water-pressure reductions.

Responses by the Brazilian national government and São Paulo state government, which oversee the large-scale management of the reservoir systems that feed the São Paulo metropolitan region, included expanding the interbasin conveyance capacity to allow for larger water transfers.

Status

Although reducing water demand, repairing leaks, and diversifying water supplies helped mitigate the worst effects of the drought, the crisis ultimately ended when normal rainfall returned to the region in 2016 and helped replenish the Cantareira reservoir system.

SABESP subsequently implemented a strategic plan to help mitigate the effects of future droughts. This plan involved institutional strengthening, pathways for public participation, tools for measuring water security, and plans for ecosystem restoration.

Organizations in the area have also invested in infrastructure improvements, such as leak repairs and water-treatment-capacity expansion. Major long-term responses by the Brazilian national and São Paulo state governments include traditional, engineered water supply capacity-building techniques, such as expanding the capacity of the conveyance structures for interbasin water transfers.

Key Insights

Because of the three main factors that led to São Paulo’s water supply crisis (drought, population growth, and system mismanagement), SABESP, along with the state and national governments, took a systems-level approach to addressing water scarcity. This involved a combination of infrastructure investments, policy changes, and ecosystem restoration.

São Paulo’s experience highlights the potential for alternative responses beyond capacity building, such as improved water-resources management, community involvement, and ecosystem restoration, each of which can be an effective long-term response.

• Infrastructure improvements require coordination: Improvements to infrastructure, including augmenting capacity for water conveyance and treatment, are needed and require coordination among city, state, and national organizations to properly function as a system. Coordination would involve updated modeling and scenario planning for water-resources management across the basins and city to enhance the overall system’s resilience to drought, the leading driver of the crisis.
• Community outreach can help reduce demand: Community involvement during the water crisis, often through social media, enabled SABESP to reduce demand by highlighting fiscal incentives for saving water, which somewhat addressed the demand on the system. However, efforts for outreach could have included more equity considerations.
• Restoring ecosystems can help boost the water supply: With a significant push by SABESP, state and national governments’ planned efforts of reforestation in watersheds feeding the reservoir systems will boost water supply in the region and mitigate the water supply’s pollution. Native forest ecosystems enable cleaner water to more gradually run off into rivers and reservoirs, which allows for more flexibility in managing the reservoir system and more-efficient water treatment.

Melbourne

Nature of the Crisis

Melbourne, Australia, is growing rapidly: Its population expanded from 3.2 million in 2001 to 4.6 million in 2024. This growth is expected to continue, with up to 6 million people living in the region by 2030 and up to 8 million by 2070.

The Millennium Drought started in 1996 and ended in 2010. Successive low rainfalls during the cool seasons led to increasingly dire hydrologic conditions, such as dried vegetation and drained groundwater resources. Reservoir storage volumes dropped from effectively full in 1996 to less than one-third by 2010, leaving only one year’s supply in storage.

Response

Melbourne took a consultative approach, and no fines were ever issued. Instead, in 2008, the city adopted a “Target 155” campaign to drop per capita water consumption amount to 155 liters per day (41 gallons per day). At the time, the average per capita consumption amount in Australia was 340 liters per day, or 90 gallons per day. The campaign resulted in per capita consumption dropping 40 percent over the last two years of the drought and yielding a net daily consumption rate of 22 percent less than the average daily rate in the 1990s.

The city also built new infrastructure. Construction began in 2009 on a seawater desalination plant, and the 70-kilometer (44-mile) North-South Pipeline from the Goulburn River was completed in 2010.

Status

The $3.1 billion desalination plant came online in 2012 but did not receive its first order to provide water until 2017. The city can now meet half its water needs with the desalination plant and Goulburn pipeline.

In 2015, rainwater tanks became compulsory in new homes, reducing laundry, toilet, and garden reliance on city water by 40 percent. The government of the state of Victoria also launched a variety of educational campaigns and efficiency rebate incentives; it also offered residents free shower-timer devices.

Despite these efforts, net annual water use increased 10.7 percent from 2019 to 2024 because of continued population growth in the region. Melbourne Water, the city water agency, provides copious monitoring data to keep the public informed.

Key Insights

• New infrastructure is needed for long-term crisis solutions: Melbourne has historically built additional water-storage capacity in part by merging with other area providers. Ultimately, the Millennium Drought showed the limits of that approach, so the city pivoted to building an interbasin transfer and a desalination plant. These were long-term solutions, however, and were less effective in solving the immediate crisis (although they seem poised to prevent the next one).
• Voluntary restrictions can yield positive effects: The collaborative and consultative approach within communities worked to reduce per capita water consumption quickly and appears to have held even after the crisis dissipated. In addition, these voluntary restrictions might have allowed for enough general goodwill from the public to fund the large infrastructure projects or try new technologies.

Response

The long-lasting megadrought has prompted a series of initiatives and investments by the city and its regional water supplier. The Southern Nevada Water Authority (SNWA), a regional water-management authority, and the City of Las Vegas have taken steps to augment the city’s water supplies and invest heavily in water-conservation measures.

These measures include two new projects to increase water-pumping capacity below Lake Meade by 900 million gallons per day (3.4 billion liters per day) and comprehensive water-conservation policies that focus on incentivizing reduced water consumption and requiring water efficiency via revised building codes.

Status

Despite continued population growth and water supply stressors, between 2002 and 2023, Las Vegas reduced its per capita water use by 58 percent. Las Vegas’s drought conditions are likely to be permanent because of the aridification of the Colorado River Basin and subsequent reductions in state-level water allocations.

As the region faces population growth and the effects of climate change, SNWA predicts an increase in per capita demand by 10 gallons per day (37.4 liters per day). Hence, reducing per capita water use remains a priority, and the city’s new per capita conservation goal will be 86 gallons per day (325 liters per day) by 2035.

Key Insights

• Proactive planning and investment pay off: Las Vegas credits its water resilience to proactive planning and investment. SNWA updates its 50-year long-term plan annually, integrating new climate and population projections and state-of-the art modeling techniques to develop various supply and demand scenarios to ensure that the city is prepared for a variety of possible futures. To enable such frequent long-term planning, SNWA has invested in significant staff capacity and technical expertise to understand the models that inform the plan.
• Education and communication are critical for intergovernmental coordination: SNWA’s governance structure requires extensive intergovernmental coordination, with each participating municipality required to sign off on any regional water policies or investments. This has required SNWA to focus heavily on education and communication to diverse constituencies.

Lessons Learned

Lesson 1

Plan and Invest Proactively

The first lesson is the central importance of planning ahead and investing early to mitigate future risks. Lack of prior planning and investment was often cited as contributing to the crisis occurring in the first place, and any prior planning that had been done was usually useful only for responding to the crisis.

What seems like an acute event is often a slow-onset disaster; cities often receive signals that there are challenges to the water supply coming but might delay a response until the situation is dire. Lag time between making a decision about water supplies and realizing the decision’s benefits might jeopardize water security during a water supply crisis.

Additionally, decisions made about water supplies and management responses during a crisis are made quickly and, therefore, are likely to lack the evaluation and community engagement needed for truly effective and resilient investments.

Lesson 2

Take a Systems-Level Approach to Urban Water Security

Building urban water security requires a systems-level approach and a shift in thinking from a single emphasis on supply augmentation to a broader view of sustainable and adequate water availability. The value of this shift to a more systems-based approach is a lesson many of the cities in our case study learned during their water supply crises. Specifically, they learned the importance of cross-departmental collaboration, building data systems and technical capacities, and ensuring financial resilience.

It can be challenging to work effectively across departments on a new or shared goal, however, because there is a need to balance respect for domain expertise with the reality of new, cross-cutting objectives. Investments in these relationships and capacities can pay off in both planning for and responding to a crisis. As one decisionmaker put it, "Investments in transversal capabilities are never wasted—that’s your disaster response team."

Lesson 3

Strengthen Collaboration Between Governments

Building urban water security cannot be done by a city government or water agency alone; it requires strong coordination and partnership across governments (horizontally and vertically). The systems, investments, and behaviors needed for urban water security often engage national, subnational, and local governments and involve partnerships with nongovernmental organizations, community organizations, and the private sector.

Urban water security—and an effective crisis response—requires financing, regulation, and technical resources that are often best provided by multiple levels of government. National and subnational governments have a strong stake in the development and resilience of urban water systems and the long-term sustainability of urban areas.

Lesson 4

Embrace Innovative Solutions for Resiliency That Fit the Context

Technological solutions such as desalination, advanced modeling, and demand-reduction systems, can play a critical role in building urban water security and are constantly evolving. Some solutions might be at the small scale of networked sensors or new materials, and others might require systemic approaches, such as water-pricing markets or new analytical modeling techniques. This means that decisionmakers must not rely only on what has worked in the past or the usual responses and tools.

Innovative solutions could also include newly socialized concepts, such as rainwater harvesting and graywater recycling; land-use reforms, such as green infrastructure; or planning approaches that focus on resource recovery or even zero-liquid discharge. Embracing and implementing new approaches will require collaborative public-private partnerships and building trust well in advance of any potential crisis.

Lesson 5

Build Trust and Effective Communication

Perhaps the most common and challenging lesson learned from experiences with water supply crises is the importance of building trust and communicating effectively with city residents.

Decisionmakers often struggle with the need to be straightforward and honest with residents about a water system’s condition, the threats it faces, and the investments and changes needed to ensure water security. It takes political courage to communicate clearly and accurately about water supply challenges, and urban water suppliers often lack experience with public engagement and communication

Water crises do not affect everyone in a community equally; often, long-standing social, economic, and political inequities are reflected in the quantity and quality of water that people can access. Those who already experience vulnerability are therefore likely to experience the effect of significant water shortages “first and worst.”

Building trust among affected communities fosters collaboration and ensures that solutions are equitable and sustainable. This involves transparent communication, consistent engagement, and accountability from decisionmakers. Including multiple voices in decisionmaking processes means actively involving community leaders, local organizations, and residents in discussions and planning.

Catalyzing Change with Pathways to Urban Water Security

How do leaders, decisionmakers, and residents integrate these lessons for their own cities? Perhaps the biggest challenge cities face is sustaining attention and resources when there is not an emergency.

Mobilizing the resources and expertise needed to make these shifts will require strong local leadership, public awareness, and intergovernmental support. Creatively and effectively communicating the importance of building urban water security and the investments it entails is critical.

Cities around the world are actively grappling with major challenges to their water supplies. From Beijing to Montevideo, and from Mexico City to Bengaluru, water security is on the agenda. Cities make headlines when water supplies fall dramatically during a drought, but building urban water security is not a task solely for these extreme cases and it cannot be achieved effectively during a crisis.

Because temperature and precipitation patterns are shifting, cities that have historically not needed to worry about reliable water supplies might see new challenges emerge. Population growth, aging infrastructure, and siloed decisionmaking can also leave systems vulnerable to climate events that historically caused little stress. Building urban water security gives decisionmakers the tools and capacities they need to avoid a crisis and respond effectively when major supply stressors do occur.

Each city will have its unique pathways to urban water security. Some cities will need to focus on building the human and technical capacity needed to undertake long-term planning, while others might need to prioritize intergovernmental collaboration or capital investments. Cities’ hydrological, infrastructure, financial, social, and political contexts will shape and constrain decisionmakers’ opportunities as they evaluate trade-offs and set the necessary priorities for moving toward water security.

Research at RAND is contributing to creating the frameworks and strategies that cities need to build urban water security before they face a real crisis—the next Day Zero. This project presents a first step in understanding how decisionmakers can best act now to prevent catastrophic climate risks in the future. Future research can examine the conditions that foster proactive investment and planning, the monitoring and metrics most effective for anticipating a crisis, the challenges that smaller cities and more-rural areas face, and the effective and equitable methods for assessing trade-offs. Rigorous, engaged research can continue supporting efforts to build urban water security and avoid the worst implications of catastrophic water supply risks.

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Topics

• Climatology
• Global Climate Change
• Water Resources Management
• Water Supply