by Aparna Nathan
In January 2018, Cape Town, South Africa started counting down toward “Day Zero.” It wasn’t the end of the world, but it was similarly apocalyptic: the day that the city would run out of water completely. Through discipline and technological advances, the city was able to avoid catastrophe. But that’s not the last we’ll see of water crises, and like Cape Town, we may need to rethink our relationship to this natural resource in a modernizing world.
Recently, water shortages—defined as insufficient water to satisfy residents’ needs—have become increasingly common. In 2010, the United Nations deemed water a human right; yet up to four billion people face water scarcity at least one month per year, and the World Wildlife Fund estimates that two-thirds of the planet’s population will face water shortages by 2025. Water shortages can emerge due to a growing population, disruption of natural water patterns supplying agriculture, increasing water consumption, and pollution by industrial activity. As a result, people face malnutrition and hygiene-related diseases (which kill nearly one million people per year) and undergo great physical tolls to seek out limited water resources.
Humans aren’t the only ones feeling a little parched: animals and plants also share our valuable water resources, and as these are depleted, species become at risk of extinction. Just like us, animals and plants can change their behavior to adapt to water shortages, but real evolution happens on a long timescale that can’t keep up with the rapid rise in water crises.
But some pockets of the Earth, like deserts, have always had freshwater shortages. Animals and plants that live in these climates have already had millennia to adapt, so they can serve as inspiration as humans design systems to harness water. One proposed framework defines categories of water management strategies: on the one hand are “green” strategies, which take advantage of organisms’ existing water adaptations: for example, by minimizing interference with an established ecosystem, or by planting drought-resistant crops. These are often contrasted with “grey” strategies: manmade, technology-based measures like wastewater treatment and desalination that redraw the traditional path water follows. But the division may not be as black-and-white (or, rather, green-and-grey) as it seems – sometimes, technology can actually help water run its natural course (Figure 1).
Saltwater, but hold the salt
Cape Town avoided “Day Zero” through a combination of largely grey strategies, in conjunction with intentional changes in how the city approached water usage. They restricted water use (for example, flushing toilets less frequently), reduced irrigation of fields supporting the water-guzzling wine industry, and pumped in water from surrounding areas.
One strategy that attracted a lot of attention—both praise and criticism—was desalination. This is a chemical process that makes ocean water fit to drink by removing salt that would normally make you more dehydrated if consumed. For a region like Cape Town, surrounded by the ocean, this is a seemingly ideal approach, and they aren’t the first to try it. Desalination has been used successfully in Israel, another arid but ocean-hugging region. And as with many ideas, nature thought of it first: albatrosses often only have access to salt water as they fly over the ocean, so they have special salt glands that remove the salt and excrete it as a concentrated salt solution.
Desalination uses a variety of methods to separate water and salt. One way is to boil water, which creates salt-free steam that can be condensed back into water. Another method is to pump water through a filter that lets water pass through but not salt. Both of these are extremely energy-intensive, and the salt doesn’t disappear. Just like the albatross, desalination produces a salt solution called brine, which is usually disposed back into the ocean (Figure 2). But this can disrupt aquatic ecosystems, which are already at risk because sea creatures can be sucked into the plants when the saltwater is initially collected.
Nevertheless, desalination is on the rise. The process is steadily producing a larger proportion of the freshwater that drought-prone ocean-side regions need. A desalination plant near San Diego—one of 11 in California—now processes 100 million gallons of saltwater per day, producing 50 million gallons of freshwater. It quenches the thirst of 10% of the region’s population, but ends up costing twice as much as direct freshwater sources.
Turning earth and air into water
Currently, India is undergoing the worst water shortage of its history due to insufficient monsoon rains. As millions of people are left without water, one instinct is to dig deeper. Groundwater is a hidden store of freshwater below the earth’s surface that can be accessed through wells or pumps. But as above-ground water becomes more scarce, buried stores are also dwindling. In India, where many homes and farms are supplied with well water, families are drilling deeper “bore wells.” This is similar to plants that grow longer roots in dry soil in hopes of accessing more water. But this strategy exacerbates the problem by depleting even the deeper groundwater and siphoning water away from those without bore wells.
Other strategies aim to capture water above ground using “grey” infrastructure, like pits that store excess water for drier times. But there are also green-grey hybrid strategies that don’t use technology to interrupt natural water processes; rather, technology is used to augment such processes. For example, rainwater can be re-routed to groundwater by collecting and filtering it through plants on green rooftops or rain gardens. This avoids the production of contamination-prone run off.
Even more creative hybrid approaches are literally trying to make water out of thin air — specifically, from fog. Some areas, like the Atacama Desert in Chile, receive just millimeters of annual rainfall but see water-dense fog for much of the year. One cubic meter of fog can contain up to 0.5 grams of water, and while that doesn’t sound like much, it adds up when it blankets a large expanse of land. The simplest version of a fog catcher is a mesh screen that traps water from the air in its holes. This requires no electricity or technological expertise, and one 13 foot by 26 foot panel can produce 40-200 gallons per day. Higher-tech versions can use small electric charges to attract water to the mesh, increasing the amount of water that is harvested.
Fog catching is a return to ancient methods: ancient Egyptian, Roman, and Latin American civilizations all collected condensation from fog. They may have been inspired by trees and animals like desert beetles and lizards that capture water from air using specialized appendages. Now these methods are making a comeback. They are already sprinkled across Chile, Morocco, Nepal, Ethiopia, and Guatemala, and there are plans to test them in sites in California and Arizona.
Designing bluer greenery
There is a consensus that agriculture is one of the major contributors to the water shortage because of the massive water supply required to keep vast crop fields fertile. Agricultural water usage can become “smarter,” however, by using sensors to measure rainfall and soil moisture to avoid overwatering plants. Soil composition can determine water retention and is affected by the types of plants, so rotating through specific sequences of plants or fortifying the soil with organic matter—like compost—can maximize the soil’s water storage potential. Certain crops, like chickpeas and chia, are naturally more drought tolerant, and although genetically-modified organisms remain controversial, common crops like corn and rice can be made more drought-tolerant by making edits to their genomes. These changes bestow on them traits more common among desert plants, like the ability to use 80% less water by being more metabolically active at night (when water loss due to heat is less likely), or quickly bouncing back after drought-induced dormancy.
Groundwater alone cannot sustain the growth of large quantities of crops in a limited area, so irrigation artificially re-routes natural bodies of water, denying wild plants their normal water supply. But this is just one example of how human manipulation of fauna has interfered with the water cycle. Humans have also increased the water burden by growing non-native, maladapted plants as part of custom landscaping projects.
The root of the matter—quite literally—in both of these cases is that plants have evolved adaptations to survive in their ecosystems. A plant that normally grows in the desert has long roots and a waxy coating to conserve water, while a plant that normally grows in a rainforest has leaves that can shed excess water instead. Transplanting one of these into a foreign ecosystem would dramatically change water usage in the soil. Additionally, invasive plants tend to use more water as a strategy to outcompete native plants. In Cape Town, the Greater Cape Town Water Fund Business Case estimated that invasive plants like acacias, pines, and eucalyptus use more than 15 billion liters of extra water. Removing invasive plant species could be an effective green strategy to conserve water in residential areas.
Water has always been essential to life on Earth—it’s one of the things that makes our blue planet so special. But now, the Earth is drying up, and humans, other animals, and plants must jointly face an impending and accelerating water shortage. Fortunately, there are changes we can make to reduce our water consumption. Since both grey and green methods have their own strengths and weaknesses, the most effective solution might require a combination of technology and nature’s own tricks to restore an equilibrium.
Aparna Nathan is a third-year Ph.D. student in the Bioinformatics and Integrative Genomics program at Harvard University. Follow her on Twitter at @aparnanathan.
For More Information:
- Read the United Nations’ World Water Development Report to learn more about potential solutions to water scarcity and inequity across the globe
- Check out this article about how South Africa came back from the brink of “Day Zero.”
- To see desalination at work, watch this video of the Sorek desalination plant in Israel.
This article is part of our special edition on water. To read more, check out our special edition homepage!