8.11: The Global Water Crisis

Despite the seeming abundance of water, as many as four billion people experience severe water shortages at least one month out of the year. From one to four billion people struggle to find water at any time of the year. At least 193 cities in 16 countries representing a third of the world’s population lack sufficient water for drinking, agriculture, and industry (Mekonnen and Hoeskstra 2016; He et al. 2021). Major cities such as Cape Town, South Africa; São Paolo, Brazil; and Chennai, India, face what has come to be known as Day Zero, the day that a city’s municipal water supply runs dry. An assessment of water supply and demand in a dozen megacities—cities whose populations exceed 10 million—revealed that 11 of them currently use more water than they can supply (Ahmadi et al. 2020). The lack of water for billions of people across the globe has been called the global water crisis, a term that emerged in the 1990s (Bruns and Frick 2014).

“All Water Problems Are Local”

Though important, the notion of a global water shortage “is of little practical utility,” according to Gleick and Palanniappan (2010). That’s because supply and demand aren’t matched on global scales (Gleick 2018). With few exceptions, humans obtain their water near a local source: the ground, a lake, a river, a reservoir. As Charles Fishman, author of The Big Thirst: The Secret Life and Turbulent Future of Water (2011), puts it, “All water problems are local.”

The availability of water in a region depends on three major factors (following Gleick 2018):

• The operation of the water cycle—the relative rates of evaporation and precipitation that remove water from and add it to a reservoir.
• The demand for water—a complex function of population size, primary uses of water (e.g., household, agricultural, or industrial), social factors (e.g., landscape types, rural-to-urban transition), and economic factors (i.e., adoption of water reclamation and conservation technologies).
• The availability of technology for improving water use or supply.

Though highly simplified, this conceptual model of water supply helps frame the problems facing management of water resources.

Water Scarcity

The mismatch between supply and demand on a regional basis drives water scarcity—a lack of sufficient water in a region for any number of purposes (e.g., United Nations 2023). Shortages of water raise issues of water security, the ability of a community to protect access to sustainable quantities of water for practical and peaceful purposes (e.g., United Nations University 2013). In places where water scarcity is prolonged or severe, disputes over water—water conflicts—may occur.

Though other sociopolitical issues contribute to tensions between countries, states, or groups, scarcity has arguably led to an increase in water conflicts since the 1990s (e.g., Levy and Sidel 2011). Most disputes can be settled peacefully, but some—such as the conflicts in Syria and Yemen affecting tens of millions of people—underscore the ways in which water scarcity can ignite tensions and fuel violence (e.g., Gleick 2014). In such conflicts, water and water-generated energy supplies (i.e., dams) become centerpieces of military tactics for gaining an advantage over an enemy. Unfortunately, civilian populations suffer the most in these conflicts. Despite the challenges, there is hope for “peaceful sharing and management of water” in at least some parts of the world (e.g., Boretti and Rosa 2019; Angelakis et al., 2021; United Nations 2022).

Desalination: Freshwater from the Ocean

A full exploration of the ways in which governments and municipalities are grappling with water shortages is beyond the scope of our discussion here. But one strategy in particular has gained attention in recent decades. Because it involves salts and the ocean, I include it here.

With water supplies increasingly vulnerable to climate change, or where other water resources are scarce or limited, desalination—the removal of salts from seawater to produce freshwater—has emerged as one solution (e.g., Darre and Toor 2018; Eke et al. 2020). In extremely arid countries—such as Qatar, Kuwait, the United Arab Emirates, and Saudi Arabia—desalination provides more than half of the freshwater needs (e.g., Darwish et al. 2012; Mannan et al. 2019; Tariq et al. 2022).

More than 20,000 desalination plants—currently operational or under construction—exist in 181 countries around the world, including the United States (e.g., Eke et al. 2020). In fact, the US generates more than 11 percent of the freshwater produced globally. Florida, California, and Texas account for most desalination (68 percent), but plants can be found in 32 other states as well (as of 2018; see Mickley 2018). California hosts a dozen existing and four proposed desalination plants (California Water Boards 2023b). The largest plant can be found in the US in Carlsbad, California, which supplies 400,000 San Diego County residents with about 50 million gallons of water daily (California Water Boards 2023a). Though not without controversy, two additional seawater desalination facilities are planned for Southern California: the West Basin Ocean Water Desalination Project (El Segundo) and the Doheny Ocean Desalination Project (Dana Point). On December 9, 2022, the California State Lands Commission approved a permit for construction of the Doheny plant. Once operational, the facility will supply five million gallons of water daily (South Coast Water District 2023).

Theoretically, the supply of water available for desalination is as big as the ocean. Unlike technologies that recycle wastewater, desalinated water is “new” water. It doesn’t depend on evaporation and precipitation via the water cycle. It’s also relatively climate-independent. Desalination can be maintained regardless of changes in climate as long as an energy source is available (e.g., Jones et al. 2021; Ghazi et al. 2022).

Desalination technologies generally fall into one of two categories: (1) thermal-based desalination, heating and evaporating seawater and recovering the water vapor; and (2) membrane-based technologies, using pressure to push seawater through a semipermeable membrane, a kind of filter which separates the salts from the water. Thermal technologies—the oldest form of desalination—work well in locations, such as North and East Africa and the Middle East (e.g., Xu et al. 2013; (Reif and Alhalabi 2015). Thermal-based desalination plants are often built adjacent to power plants to ensure a steady supply of energy. Membrane-based desalination plants have a lower energy requirement—though still high compared to conventional ways of obtaining water (e.g, Voutchkov 2018). This makes them more popular outside of the Middle East. The highest percentage of existing and planned desalination plants use membrane technologies (e.g, Eke et al. 2020).

Among membrane-based technologies, reverse osmosis systems (RO)—moving water against a concentration gradient (the opposite of osmosis)—are the most popular. In fact, RO systems exist for household, industrial, and military water purification. As described in Darre and Toor (2018), RO desalination plants typically require pretreatment of the intake seawater to remove particles, microbes, and other substances that may foul the membrane filter. The pretreated water is then pumped at high pressure through a membrane with pores large enough to permit water molecules to pass but too small for salts. The process results in production of both freshwater and brine.

A number of economic, technical, and environmental challenges complicate the acceptance of desalination as a competitive and sustainable source of water (e.g., Xu et al. 2013; Darre and Toor 2018). Its high energy requirements have raised concerns over costs in a future with rising energy prices. Plants may also produce greenhouse gas emissions in a world increasingly seeking to reduce them. Aende et al. (2020) note that the energy used by the Carlsbad desalination plant could power 20,000 homes. While solar-powered desalination plants hold promise, a number of factors, including intermittent availability of the Sun and seasonal and latitudinal variations in solar intensity, continue to hamper their implementation.

Disposal or reuse of brine—the salty syrup that remains once water has been extracted—has also been raised as a concern (e.g., Jones et al. 2021). In high-energy coastal environments, brine may be piped through diffusers, which help to mix and dilute it in the surrounding seawater. But this option is not available in low-energy environments, where toxins in the brine may harm marine organisms (e.g., Darre and Toor 2018; Delgado et al. 2020). In some cases, brine may be converted to rock salt and other products, but the volume of brine produced may exceed demand (e.g., Xu et al. 2013).

Finally, pumping seawater from the ocean may unintentionally remove large quantities of plankton and larvae that form the base of marine food webs. Prior to construction of the Carlsbad plant, scientists raised concerns about potential negative effects on the productivity of a nearby marine protected area (e.g., Darre and Toor 2018).

Future proposals for desalination plants will continue to raise concerns about cost effectiveness, energy demand, greenhouse gas contributions, brine disposal, and harm to the marine environment, especially in California. The Huntington Beach desalination plant—first proposed in 1998—met with considerable opposition from environmental groups, citizens, and taxpayer groups. They argued that the plant would raise water costs, displace Latine neighborhoods, and harm marine life (Symon 2020). Proponents argued that desalination is necessary to avert water shortages (Alvarado 2020). Ultimately, the Coastal Commission rejected the project in May 2022 (Becker 2022).

Despite the negative perceptions of desalination, some researchers argue that these challenges can be overcome. As renewable energy sources develop and brine disposal methods improve, the costs and environmental harm of desalination will be reduced (e.g., Pistocchi et al. 2020). Like any new technology, desalination will benefit from ongoing critical review and additional research to overcome its challenges (e.g., Darre and Toor 2018). However, like any technological fix, desalination may be a temporary solution. Ultimately, humans will need to make difficult choices about how we create a sustainable water supply in the 21st century (e.g., Pistocchi et al. 2020).