The Water Cycle Is Broken, But We Can Fix It

  • March 13, 2019
  • by Sandra Postel

By working with nature, rather than against it, we can replenish the world's water supply.

When it comes to water, the past is no longer a good guide for the here-and-now, much less for the future.

In the spring of 2018, Cape Town, South Africa, narrowly escaped shutting off drinking water taps for its 4 million residents. Three consecutive years of drought had dried up its reservoirs. City officials began publicly announcing “Day Zero”—the date water would no longer flow to household faucets. At that point, residents would need to retrieve their rations of drinking water from one of 200 distribution stations around the metropolis.

Fortunately, nature bailed out Cape Town just in time.  Stricter conservation measures combined with the purchase of agricultural water enabled the city to keep pushing Day Zero out—and then, luckily, the rains returned. But the scare was a wake-up call for mayors and utilities everywhere: When it comes to water, the past is no longer a good guide for the here-and-now, much less for the future.

Nothing is more critical to the success of a society than its ability to supply water where it is needed, when it is needed, and, on the flip side, to keep floodwaters at bay. History is studded with enterprising cultures that failed this basic challenge—from the Sumerians of ancient Mesopotamia, the first irrigation-based society, to the Hohokam of the American Southwest, which enjoyed a 1,000-year run in what is now central Arizona.

On the face of it, global society today would seem to have licked the water-security challenge. Some 58,000 large dams capture flood runoff, store water for later use, and allow engineers to turn major rivers on and off like plumbing works. Cities worldwide import the equivalent of 10 Colorado Rivers to meet their annual water needs; if positioned end to end, the canals and pipelines transporting that water would stretch halfway around the world. Huge pumps draw water from beneath the earth to irrigate crops that help feed the world. Indeed, it is hard to imagine our world of 7.6 billion people and $75 trillion in annual economic activity without this vast network of impressive water engineering.

Data Points

  • 48% of the volume of river flows globally are disrupted by dams and reservoirs.

    This is up from 5 percent in 1950.

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  • 1/10 of global food production depends on the depletion of groundwater.

    Groundwater depletion is rampant across important food-producing regions of China, India, Pakistan, Iran, the Middle East, Mexico, and the U.S.

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Yet the command-and-control style of water management that took hold during the 20th century entails a Faustian bargain: While it has brought much of the world enormous prosperity, it has broken the water cycle—the natural storage and movement of water between the land, sea, and air that sustains life and is critical to that human prosperity. An unsettling number of large rivers—including the Colorado and Rio Grande in the U.S. Southwest, the Ganges and Indus in South Asia, the Amu Darya in central Asia, the Yellow in northern China, the Nile in northeastern Africa, and the Murray in southeastern Australia—are now so over-tapped that they drop to a trickle or dry up completely for long periods of time. Globally, dams and reservoirs now disrupt 48 percent of the volume of river flows, up from 5 percent in 1950. This flow disruption is a major reason freshwater vertebrate populations have declined by 83 percent since 1970. Dams have also trapped more than 100 billion tons of sediment that rivers would otherwise carry toward the sea to replenish deltas and sustain ecosystems critical to fisheries.

The depletion of groundwater—those hidden reserves beneath the earth—is now the sleeping tiger of global water risks. In many parts of the world, groundwater pumping exceeds recharge, causing water tables to drop and underground water reserves to shrink. Groundwater depletion is rampant across important food-producing regions of China, India, Pakistan, the Middle East, Mexico, and the United States. About one-tenth of global food production depends on
the depletion of groundwater—a hidden water debt that threatens food security and agricultural economies.

The world’s soils, another critical part of the water cycle, can theoretically hold eight times more water than all rivers combined. Yet the deep plowing and monoculture cropping methods employed by industrial agriculture have led to severe soil erosion and loss of organic matter, shrinking the natural soil reservoir. This means farmers have less resilience to dry spells. As Jerry Hatfield, director of the U.S. Department of Agriculture’s National Laboratory for Agriculture and the Environment in Ames, Iowa, has put it: “We’re losing 20 percent of our crop 80 percent of the time due to temporary water shortage.”

With more than half the world’s wetlands sacrificed to development and cropland expansion, nature’s way of capturing, storing, and purifying runoff has been lost in many locations. Besides worsening both floods and droughts, this wetland loss has allowed large quantities of nitrogen and phosphorus from farm fertilizers to drain directly into rivers and streams, which then carry these pollutants to the coasts.  There, they fuel algal blooms that deplete oxygen levels as the algae decompose, threatening fish and other aquatic organisms. More than 400 dead zones now line the coasts, most in the Northern Hemisphere.

Virtually all of the consequences of this broken water cycle will worsen with climate change. As rainfall intensifies, flood damage will rise. As droughts worsen, river flows will further diminish. As wildfires burn hotter and spread farther, runoff filled with sediment and debris will threaten drinking water for communities downstream. These kinds of threats are not hypothetical: In 2017, the costs of U.S. climate- and weather-related disasters totaled a record-breaking $306 billion.

It’s tempting to try to solve our water problems with bigger dams, deeper wells, and longer water transfers. But as Albert Einstein reminded us decades ago, “We can’t solve problems by using the same kind of thinking we used when we created them.” That means thinking differently about how we use, manage, and value water. And it means figuring out how to repair and replenish the water cycle even as we prosper. It’s a tall order. But some pioneers are showing the way.

In the Verde Valley of Arizona, as in much of the western United States, farmers irrigate their fields much the way their late 19th-century predecessors did: They divert most of the flow from their local river into a ditch system that delivers water to their farmland. In the case of the Verde River, a tributary to the Colorado and a lifeline for migratory birds and wildlife in the American Southwest, those diversions often left five or more miles of the river nearly dry.

We can’t solve problems by using the same kind of thinking we used when we created them.

When tasked by The Nature Conservancy of Arizona with protecting this biological hotspot, hydrologist Kim Schonek worked closely with local irrigators to establish mutual trust and to search for a solution. The result was the installation of a solar-powered, automated head gate on the ditch system that enabled the irrigators to take just the water they needed while leaving the rest for the river. Parts of the Verde now have twice as much summertime flow as before. The result was a triple win: The irrigators got a system upgrade, the local community got a healthier river for recreation and tourism, and birds and wildlife got healthier habitat.

That success fostered other creative solutions— such as switching from flood to drip irrigation,  and diverting water from different locations—to keep the Verde flowing. One entrepreneurial conservationist motivated farmers to plant barley, which requires less summertime irrigation than many other crops, by building a local barley malting facility that supplies Arizona craft breweries.

As a result, the Verde River has become a model for smarter water management. But it took collaboration, not only between farmers and conservationists, but also with corporations wishing to invest in a healthier river. Some half a dozen companies with operations in the greater Phoenix area—including Coca-Cola, Intel, and REI—have invested in projects to keep the Verde flowing in order to enhance water security, ensure good recreational opportunities for their employees, and advance water stewardship by returning some water to the environment.

In nature, the saying goes, there is no waste.

Six years into the record-breaking Millennium Drought that hit much of Australia between 1996 and 2010, the managers of the Pennant Hills Golf Club near Sydney took this sentiment to heart. With reservoirs around the city at record low levels, they faced the prospect of dramatic water cutbacks that could turn their beloved greens to ugly browns. So club managers took an unusual step: They requested permission to tap into the sewer line that ran beneath the golf course, treat the sewage on-site, and use it to irrigate the greens.

Despite its yucky name, “sewer mining,” as the Aussies call it, is catching on, not only in Australia but around the world. It’s a way of closing the urban water loop and taking the waste out of wastewater. The pipe beneath Pennant Hills runs to the coast, where the sewage gets only basic treatment before being dumped into the Pacific Ocean. So the golf club not only decreased its potable water use by 92 percent, it reduced pollutants headed to the sea.

In contrast to conventional wastewater reuse projects, which typically collect urban wastewater and send it some distance to a large treatment plant, sewer mining is decentralized and localized, which saves energy as well as water. Stuart White, director of the Institute for Sustainable Futures at the University of Technology Sydney, sees “small-scale, modular, localized wastewater treatment” as a core element of the next generation of water infrastructure.

The Pennant Hills system involves a membrane bioreactor that treats the waste biologically and then sends the resulting product through a membrane that blocks all but the partially treated sewage. The sludge, about 2 percent of the original sewage, returns to the sewer while the treated wastewater is disinfected and sprinkled onto the gardens and greens.

Although the membrane bioreactor process has been in use for several decades, its costs and energy requirements have come down substantially in recent years. It is now treating wastewater for reuse in an apartment complex in the Battery Park neighborhood of New York City, in a mixed-use development in Victoria, British Columbia, and a high-end community in Fulton County, Georgia, to name a few.

As water supplies tighten and droughts and floods worsen, many cities are embracing a concept known as One Water—a more holistic approach to the planning and management of water supply, wastewater, and stormwater. China, for example, has launched a “sponge cities” initiative that aims to turn stormwater from a nuisance into an asset. Over the past 35 years, Chinese cities have more than tripled in number, and the nation’s urban landscape has grown by 15,400 square miles—equal to 327 times the area of San Francisco. As a result, vast areas of impermeable roads, buildings, and parking lots now sit where lakes, wetlands, and woodlands once were. So instead of stormwater soaking into the earth, it now floods streets and communities—a problem common to many of the world’s cities and towns.

In 2013, when severe flooding hit some 230 Chinese cities, President Xi Jinping announced that cities should act more like sponges, absorbing rainwater instead of allowing it to surge down streets and sidewalks. Within two years the government had selected pilot sites in 16 cities, including Beijing, Guangzhou, Shanghai, and Wuhan. The goal, an ambitious one, is to have 20 percent of each pilot city meeting sponge-city standards by 2020.

Outside of China, the adoption of green infrastructure to repair the urban water cycle is rapidly catching on, as well. In the U.S., Philadelphia plans to invest some $2 billion in rain gardens, tree trenches, wetlands, permeable pavement, vegetated swales, and other projects that encourage rainfall to infiltrate rather than run off the cityscape. The city hopes to reduce storm-related sewer overflows by 85 percent within 25 years. Green infrastructure is also a major component of Los Angeles’ effort to reduce its long-distance water imports by half by 2035. Engineering professor Richard Luthy of Stanford University estimates that by that time, the retention and underground storage of stormwater could meet 14 to 28 percent of the city’s water needs.

While big dams and desalination plants are flashier solutions to water shortage, conservation and efficiency measures remain the most cost-effective and environmentally sound ways to meet new water demands—and they are far from tapped out. In the United States, domestic water use per person fell 18 percent between 2000 and 2015, and will continue to fall. The major reason is the 1992 passage of national water efficiency standards that required plumbing manufacturers to reduce the volume of water used by toilets, urinals, faucets, and showerheads. These requirements effectively built conservation into new and remodeled homes and buildings and are now saving the nation 7 billion gallons per day, according to water conservation engineer Amy Vickers, who wrote the efficiency standards. That’s equivalent to seven times the daily water use of New York City.

As water supplies tighten and droughts and floods worsen, many cities are embracing a concept known as One Water—a more holistic approach to the planning and management of water supply, wastewater, and stormwater.

With the addition of efficiency standards for clothes washers and dishwashers, along with the 2006 launch of the Environmental Protection Agency’s WaterSense, a voluntary labeling program that helps consumers choose water-efficient appliances, the savings continue to grow. In the coming decades, researchers expect indoor water use per person to drop an additional 37 percent or more. In residential areas, the new conservation frontier is outdoors, since watering grass and landscaping often accounts for half or more of home water use. Many utilities, especially in the drier west, offer incentives for homeowners and businesses to shift away from thirsty grasses toward native, drought-tolerant plants.

With agriculture accounting for 70 percent of global water use, improving nutritional value per drop is critical to feeding the world while repairing the water cycle. Healthier soils with higher carbon content are capable of storing more moisture, reducing the need for irrigation and building resilience to drought. Rain-fed croplands in particular can benefit from the planting of cover crops that improve soil health and hold soil in place. Only about 3 percent of the nation’s farmland has cover crops now, suggesting a big window of opportunity. 

In the southeastern United States, where rivers and streams are home to some of the most biologically diverse fish and mussel populations, researchers are partnering with farmers to test smarter irrigation systems that tailor water delivery to actual field conditions.

In the lower Flint River Basin of southwestern Georgia, for example, heavy groundwater pumping to irrigate cotton and peanuts depletes the base flows of rivers and streams, jeopardizing threatened mussel populations. Researchers are trying variable rate irrigation, which involves programming a center pivot sprinkler equipped with a GPS system to stop spraying when it passes over a rocky section, a wetland, or any area not growing crops. That alone can often reduce water use by 15 percent. Adding soil moisture sensors to the field and setting the sprinkler to deliver only as much water as the crops actually need also boost savings. Experiments at cotton and peanut farms by University of Georgia researchers have found that these systems can increase water productivity—crop per drop—by as much as 40 percent.

Fixing the water cycle requires scaling up these promising methods, which in turn requires economic incentives and support. Government policies that incentivize more sustainable agriculture could make a big difference, as could better zoning and land-use planning that conserve and restore floodplains and wetlands. Many businesses support these efforts because they recognize that a secure water supply is critical to their bottom lines. General Mills, for example, is supporting restoration projects in watersheds where its facilities are located and investing $3.2 million to improve the health of soils on farms in its supply chain. Coca-Cola partners with conservation organizations to restore depleted rivers and wetlands to balance the water used in making its beverages.

All of this shows that our broken water cycle can be fixed if we change our thinking and encourage these new methods. The 20th century was the age of dams, diversions, and depletion, but the 21st century can be the age of replenishment, the time when we apply our ingenuity to working with nature rather than against it. With droughts, floods, and wildfires poised to worsen and spread, investing in a healthier water cycle may be the best insurance policy money can buy.