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Water Supply Problems: Resource Depletion
Freshwater supplies can be depleted when water is withdrawn faster than natural processes can replace it. One common example is groundwater mining, which occurs when groundwater is pumped from an aquifer faster than it is replenished. Pumping from a water well creates a localized lowering of the water table called a cone of depression. When many wells withdraw groundwater over a long period, the regional water table can decline substantially. As groundwater levels fall, wells may need to be drilled deeper, increasing costs and sometimes accessing more saline water.
Surface water can also be depleted through overuse. Many rivers, lakes, and reservoirs experience declining water levels when withdrawals exceed replenishment. Some major rivers, including the Colorado River in the United States and the Yellow River in China, have periodically failed to reach their usual endpoints because so much water is diverted for human use. Lake systems can also shrink due to excessive water withdrawals, as illustrated by the dramatic decline of the Aral Sea. In addition, glaciers that supply freshwater to downstream communities are shrinking because of accelerated melting associated with climate warming.
Groundwater depletion creates several additional environmental challenges. Along coastlines, excessive pumping of freshwater aquifers can lead to saltwater intrusion, a process in which seawater moves into freshwater aquifers and contaminates water supplies. Lowering the water table can also alter groundwater flow patterns. In some cases, pollutants that would normally move away from a well may instead be drawn toward it.
A declining water table can also cause the land surface to sink. Subsidence is the gradual sinking of land over a broad area, whereas sinkholes are sudden collapses that occur over a smaller area. Both can damage infrastructure, alter drainage patterns, and increase the costs of managing water resources (figure \(\PageIndex{a}\)).
Figure \(\PageIndex{a}\). Formation of a Cone of Depression around a Pumping Water Well. Image: By Tara Gross - https://www.usgs.gov/media/images/co...level-lowering, Public Domain, [https://commons.wikimedia.org/w/inde...rid=146710900]The Global Water Crisis
The water crisis refers to the growing challenge of providing sufficient quantities of clean, accessible water for people and ecosystems. Water shortages, also called water scarcity, can result from either a lack of available water or limited access to safe water supplies.
Two forms of water scarcity are commonly recognized:
- Physical water scarcity: insufficient water is available to meet demand.
- Economic water scarcity: water is available, but infrastructure, governance, or financial limitations prevent access to it.
Water stress is generally greatest in regions with low precipitation, high population densities, or both. Arid regions of North Africa and the Middle East experience some of the highest levels of water stress, while rapidly growing populations in parts of Asia have increased demand on already limited freshwater supplies.
Climate change is expected to worsen water scarcity in many regions. Changes in precipitation patterns may increase drought frequency in some areas, while shrinking mountain glaciers may reduce streamflow during dry seasons. Rising sea levels can also increase saltwater intrusion into coastal aquifers, further reducing freshwater availability (figure \(\PageIndex{b}\)).
Figure \(\PageIndex{b}\). Map of global water stress (a symptom of water scarcity) in 2019. Water stress is the ratio of water use relative to water availability and is therefore a demand-driven scarcity. Image by Genetics4good, GFDL [http://www.gnu.org/copyleft/fdl.html], via Wikimedia Commons. Water scarcity can affect food production, human health, economic development, and political stability. Because many rivers and aquifers cross political boundaries, competition for freshwater can contribute to regional tensions. Areas that have experienced disputes related to water use include the Nile River Basin in Africa, the Euphrates and Tigris Rivers in the Middle East, the Ganges River system in South Asia, and the Aral Sea Basin in Central Asia.
Moving Toward Sustainable Water Use
Addressing water scarcity requires a combination of technologies, policies, and conservation practices that reduce demand and protect freshwater systems.
Dams and Reservoirs
Dams create reservoirs that store water during wet periods and make it available during dry periods (figure \(\PageIndex{c}\)). Reservoirs can provide drinking water, generate hydroelectric power, reduce flooding, and support recreation.
However, reservoirs can have environmental costs. Water stored in reservoirs may be lost through evaporation, especially in arid climates. Dams also alter river ecosystems, change fish migration routes, and modify downstream sediment transport and river flow patterns.
Figure \(\PageIndex{c}\). Parker Dam on Lake Havasu at the start of the Colorado River Aqueduct. Image credits Erin Rempala (CC BY-NC-SA 4.0). Aqueducts and Water Transfers
Aqueducts transport water from regions where water is relatively abundant to regions where demand is high. These systems support agriculture and urban development in areas with limited local water supplies. California has several major water-transfer systems, including the Colorado River Aqueduct, the State Water Project, the Los Angeles Aqueduct, and the San Diego Aqueduct.
Water-transfer projects can be controversial because diverting water from one watershed may reduce water availability and alter ecosystems in another. Before water diversions began, the Owens Valley was a productive agricultural region where farms and ranches relied on the Owens River for irrigation and livestock production. In the early twentieth century, the City of Los Angeles purchased land and water rights throughout the valley and diverted much of the river's flow through the Los Angeles Aqueduct to meet the city's growing water demand.
These diversions contributed to the desiccation of Owens Lake and lowered water levels in Mono Lake, causing ecological damage and reducing water availability for local communities. After years of legal challenges and environmental advocacy, conservation measures and water-management agreements helped stabilize Mono Lake and partially restore its ecosystem. Owens Lake, however, remains largely dry and requires ongoing dust-control efforts because winds can carry fine sediments from the exposed lakebed into surrounding communities.
Another major example is the Colorado River Aqueduct, which transports water from the Colorado River to Southern California (figure \(\PageIndex{d}\)). Completed in 1941, the aqueduct carries water approximately 252 miles (406 km) across deserts and over mountain ranges to supply communities in the Los Angeles metropolitan area and other parts of Southern California. This engineering project helped support the rapid growth of cities in one of the driest regions of the United States.
However, the Colorado River is shared by seven U.S. states, multiple Tribal Nations, and Mexico, making allocation of its water highly contentious. Water rights along the river were largely divided during the twentieth century using estimates of river flow that are now known to have been unusually high. Today, increasing demand, prolonged drought, and climate change have reduced river flows while agricultural, urban, tribal, recreational, and ecological water needs continue to grow. As water levels in major reservoirs such as Lake Mead and Lake Powell decline, disagreements have intensified over how limited Colorado River water should be distributed among competing users and how much water should remain in the river to support ecosystems.
The Owens Valley and Colorado River examples illustrate how transferring water between watersheds can produce both benefits and costs. Aqueducts have enabled the growth of major cities and agricultural regions in arid environments, but they have also transformed ecosystems, affected rural communities, and generated conflicts over water rights and environmental protection. Understanding these tradeoffs is an important part of sustainable water management.
Figure \(\PageIndex{d}\). Top: The California Aqueduct California Aqueduct in southern California. Bottom: Gene Pumping Station off Lake Havasu at the start of the Colorado River Aqueduct. Image credits Erin Rempala (CC BY-NC-SA 4.0).
Interactive Element: Follow the Journey of Colorado River Water
Ever wondered how water reaches Southern California's cities and suburbs from hundreds of miles away? Explore the Metropolitan Water District's interactive Colorado River Aqueduct Map to trace the 252-mile journey of water from Lake Havasu across deserts, through tunnels, and over mountain ranges to communities throughout Southern California.
Try It!
- Locate Parker Dam and the Gene Pumping Plant, where water enters the aqueduct.
- Follow the aqueduct's route across the desert to Southern California.
- Identify the pumping plants, reservoirs, and tunnels that help move water uphill and across rugged terrain.
- Consider the energy, infrastructure, and cooperation required to deliver water to millions of people in one of the driest regions of North America.
As you explore, think about this question: What are the environmental benefits and tradeoffs of transporting water hundreds of miles to support cities and agriculture in arid regions?
Desalination
Desalination removes dissolved salts from seawater or saline groundwater to produce freshwater. Because it creates a new source of freshwater, desalination can help meet water demand in coastal regions.
Despite its benefits, desalination is energy intensive and expensive compared with most conventional water sources. The process also produces concentrated brine that must be disposed of carefully to minimize environmental impacts. Desalination facilities are particularly common in arid regions of the Middle East, where freshwater is scarce and energy resources are readily available.
Water Conservation
Water conservation reduces water use while maintaining essential human activities and ecosystem functions. Conservation measures can be implemented at household, municipal, and agricultural scales.
Examples of household conservation include:
- Installing high-efficiency appliances
- Using low-flow toilets and showerheads
- Repairing leaks
- Landscaping with drought-tolerant native plants
- Reducing unnecessary water use
Agriculture offers some of the greatest opportunities for conservation because irrigation accounts for most freshwater withdrawals worldwide. Effective strategies include:
- Growing crops suited to local climate conditions
- Using efficient irrigation systems, such as drip irrigation
- Practicing no-till agriculture to reduce evaporation from soil
- Reusing treated wastewater for irrigation
Explore California Native Plants with Calscape
Looking for a beautiful, water-wise landscape that supports local biodiversity? The California Native Plant Society's Calscape Plant Finder can help you discover native plants that are naturally adapted to your local climate, soils, and wildlife. Whether you want to create habitat for hummingbirds, butterflies, native bees, or other pollinators, Calscape makes it easy to find species that match your landscaping goals.
Many California native plants are highly drought tolerant and require little to no supplemental irrigation once established, making them an excellent choice for water conservation. Native plant landscapes can also improve soil health, reduce the need for fertilizers and pesticides, and provide food and shelter for local wildlife.
In many parts of California, native plants can also be incorporated into Firewise native plant landscaping practices. Firewise landscapes are designed to reduce wildfire risk around homes by creating defensible space, using fire-resistant plant communities, and minimizing the accumulation of highly flammable vegetation. When properly selected and maintained, native plants can help create landscapes that are both ecologically beneficial and better adapted to California's fire-prone environment.
Try It! Visit Calscape.org. Search for native plants that:
- Require little or no summer irrigation
- Attract birds, butterflies, or native pollinators
- Bloom during different seasons of the year
- Can be used in a Firewise landscape
How might replacing a portion of a conventional lawn with native plants conserve water while supporting local ecosystems and increasing resilience to drought and wildfire?
Rainwater Harvesting
Rainwater harvesting captures and stores rainfall for later use before it becomes runoff. Water reuse systems can also recycle treated wastewater for irrigation, industrial processes, and groundwater recharge. These approaches reduce demand on rivers, reservoirs, and aquifers while increasing the resilience of local water supplies.
Greywater Reuse
Along with rainwater harvesting, wastewater recycling, and efficient irrigation, greywater reuse can help communities reduce freshwater withdrawals and increase the resilience of local water supplies. Greywater is household wastewater from showers, bathtubs, bathroom sinks, and laundry that has not come into contact with toilet waste. Because it typically contains fewer contaminants than sewage, greywater can often be reused for irrigation and other nonpotable applications. Greywater reuse can be particularly valuable in arid regions facing increasing water scarcity due to population growth, drought, and climate change.
Together, rainwater harvesting, greywater reuse, wastewater recycling, improved infrastructure, and sustainable management of freshwater ecosystems can help communities meet water needs while protecting aquatic systems for future generations.
Groundwater Recharge
Groundwater recharge is the process by which water moves from the land surface into the ground and replenishes aquifers. Recharge occurs naturally when precipitation infiltrates the soil and percolates downward through porous rock and sediment. In many regions, however, urbanization has reduced natural recharge because roads, parking lots, and buildings prevent water from soaking into the ground.
Communities can enhance groundwater recharge through a variety of strategies. These include protecting open spaces and wetlands, using permeable pavement that allows water to infiltrate the soil, installing bioswales and rain gardens to capture and filter stormwater, directing runoff into infiltration basins, and recharging aquifers with highly treated recycled water (figure \(\PageIndex{e}\)). These green infrastructure approaches increase infiltration, improve water quality, and reduce flooding while helping replenish groundwater supplies. Artificial recharge projects can help offset groundwater depletion, reduce the impacts of drought, and store water underground for future use.
Figure \(\PageIndex{e}\): Runoff from the vicinity flows into an adjacent bioswale. Image: Erica Fischer, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons [https://commons.wikimedia.org/wiki/F..._Bioswale.jpg]![https://commons.wikimedia.org/wiki/F..._Bioswale.jpg]](https://commons.wikimedia.org/wiki/File:Meridian_Hill_Bioswale.jpg]){kind=link}
Groundwater recharge provides several environmental benefits. Replenished aquifers can support drinking water supplies, maintain streamflow during dry periods, reduce land subsidence, and help prevent saltwater intrusion in coastal regions. Because groundwater is naturally protected from evaporation, aquifers can serve as important long-term water-storage systems in arid climates.
However, recharge projects must be carefully managed to prevent contamination of groundwater resources. Water used for recharge must meet strict quality standards, and land uses in recharge areas must be monitored to reduce the risk of pollutants entering aquifers.
Case Study: Building Water Resilience in San Diego County
Like many communities in the arid southwestern United States, San Diego County relies on a diverse portfolio of water sources to improve long-term water security and reduce dependence on imported water. Historically, San Diego County has relied heavily on imported water from the Colorado River and Northern California, making it vulnerable to drought, infrastructure disruptions, and changes in water availability elsewhere in the western United States. To increase local water reliability in the face of drought, climate change, and growing demand, the region has invested in several major water-supply projects that illustrate many of the water-management strategies discussed in this chapter, including desalination, potable water reuse, groundwater recharge, conservation, and diversification of water supplies.
The Claude "Bud" Lewis Carlsbad Desalination Plant, which began operation in 2015, is the largest seawater desalination facility in the United States. The plant can produce up to 50 million gallons per day (MGD), equivalent to approximately 190 million liters per day, making it one of the largest locally controlled water sources in San Diego County. By converting seawater into freshwater, the facility provides a drought-resistant water supply, although desalination requires substantial energy and produces concentrated brine (salty water left over from the process) that must be carefully managed.
The Pure Water San Diego program is designed to produce drinking water from highly treated recycled wastewater. Using advanced purification technologies such as microfiltration, reverse osmosis, and ultraviolet disinfection, the project will provide nearly half of the City of San Diego's drinking water supply by 2035. By reusing water that would otherwise be discharged to the ocean, Pure Water San Diego increases local water independence while reducing wastewater discharges. Potable water reuse is often considered one of the most sustainable approaches to water management because it treats wastewater as a valuable water source rather than a waste product.
In East County, the East County Advanced Water Purification (East County AWP) Program is developing a similar potable water reuse system to improve regional resilience. The project will purify treated wastewater to drinking-water standards and use it to replenish local reservoirs. In addition to providing a reliable local water source, the project is expected to reduce reliance on imported water and increase drought preparedness for communities in eastern San Diego County.
Groundwater recharge is also playing an increasingly important role in California water management. In San Diego County, projects that restore wetlands, floodplains, and other natural infiltration areas help increase groundwater recharge, while highly treated recycled water can be used to replenish reservoirs and aquifers. These approaches help offset groundwater depletion and provide additional water storage that is protected from evaporation.
Together, desalination, potable water reuse, groundwater recharge, conservation, and imported water supplies illustrate how San Diego County is diversifying its water portfolio to build a more resilient and sustainable water system in an increasingly variable climate.
Despite these investments, imported water from the Colorado River and State Water Project continues to supply a substantial portion of San Diego County's water demand. The region's water strategy therefore combines imported water, desalination, potable reuse, groundwater recharge, local storage, and conservation measures to improve resilience to drought and climate change.
San Diego County's experiences demonstrate that no single solution can address water scarcity. Instead, communities often combine conservation, water recycling, desalination, imported water, and ecosystem protection to create resilient water systems capable of adapting to drought, population growth, and climate change.
Attributions
This page was heavily revised and rewritten by Erin Rempala and contains adapted content from 7.2: Water Supply Problems and Solutions by Matthew R. Fisher originally licensed CC BY 4.0. Original source: https://openoregon.pressbooks.pub/envirobiology (CC BY-NC-SA 4.0).
And additional sources cited:
- Claude "Bud" Lewis Carlsbad Desalination Plant
- Pure Water San Diego
- East County Advanced Water Purification
- Metropolitan Water District of Southern California
Modified by Matthew R. Fisher from Essentials of Environmental Science(opens in new window) by Kamala Doršner is licensed under CC BY 4.0.
This page titled 10.3: Water Scarcity and Sustainable Water Management was last modified on Fri, 09 Oct 2026 18:56:02 GMT and is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Erin Rempala via source content that was edited to the style and standards of the LibreTexts platform.
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