The future of water security in Lima, Peru isn't happening in the city. It's happening 75 miles away and 12,000 feet up, in once-forgotten stone channels that pre-date the Incans.
The channels through the Humantanga district snake across steep slopes, collecting rainfall and water from highland streams during the rainy season, letting it seep into the mountain where it percolates naturally over months rather than running off through streams.
"When you see it, it's amazing and beautiful," says Leah Bremer, a researcher with The Natural Capital Project who spent years working with The Nature Conservancy and local organizations on a fund to improve water quantity and quality in the area. "Some are stone. Some are concrete. It's a combination of the natural and the more modern."
Called mamanteo—Spanish for suckling—the channels are an example of communities turning to the water wisdom of the ancients to solve shortages exacerbated by climate change. Historians believe the Wari culture built the channels as part of a complex water conservation system beginning about 1,500 years ago, centuries before the Incas. They fell into disrepair in recent centuries.
Peruvians are not the only people who have found that everything old is useful again; thousand-year-old water-saving techniques are being revived in communities in sub-Saharan Africa and India.
In Peru, the mamanteo have benefits both upstream and downstream. The people in Humantanga, a district whose name means "the place where falcons roost," have more water and better grazing for their livestock during the dry season. But it also has a profound effect downstream, increasing the quantity of water reaching Lima during the dry months of May through December.
That’s important because, despite building additional reservoirs and transporting waters through the Andes to the coast, Lima, the second largest desert city in the world, faces an annual water deficit.
Timm Kroeger, a Nature Conservancy economist who did a cost-benefit analysis, says the project would pay for itself. "It really is a no-brainer," he adds.
“Rehabilitation of ancient structures -- not the construction of new ones with the same technology -- is a very cost-effective measure,” adds Bert De Bièvre, a Lima-based researcher with the Consortium for the Sustainable Development of the Andean Ecoregion (CONDESAN). He notes, however, the both green and grey construction will be necessary to deal with Lima’s water problems.
So far, at least ten mamanteos (sometimes also called amunas) have been restored. State and national funding will contribute $23 million to green solutions. They include restoring the mamanteo system, improving local irrigation, reducing overgrazing in the highlands, and transitioning to genetically superior cows that produce more milk. More milk per cow means fewer cows stressing the highlands.
A study by Forest Trends, a nonprofit that includes environmental and industry representatives, co-authored by De Bievre found that such green interventions could address nearly 90 percent of Lima’s water flow deficit during the dry season at costs lower than or competitive with modern gray infrastructure projects like pipelines or wastewater treatment plants.
"Ancient infiltration techniques were once used to increase water storage and slowly release flow that would re-surface in downslope springs after a time lag of several months can also be part of a landscape strategy," the study notes. "Implementing these types of green interventions can result in additional social, cultural, and environmental benefits, as upstream communities are engaged to support improved management of the region’s watersheds and water resources and as natural systems can also filter out water contaminants, stabilize soils, and provide habitat for biodiversity."
Bremer says locals originally were skeptical the old ways would work, but were convinced when the grasslands stayed green during the dry season. “I think it’s really cool that it comes from traditional knowledge,” she says. “It’s amazing the techniques they had.”
Peru is just one place where communities are turning to practical, cost-efficient water saving techniques thousands of years old.
In Kenya, sand dams, which date to the Romans, are improving water security in some of the harshest areas. In colonial Kenya, people used stones to form barricades to control soil erosion, according to Joe Kiolo, the communications manager for the African Sand Dam Foundation, and noticed the area would stay green long after the rainy season.
The technology is simple. Locals construct a concrete barrier across a seasonal river flowing over bedrock. As the river flows, sand in the water is deposited behind the wall, but only a small bit of the flow is held behind. Over time, layers of sand build up, creating a reservoir that stores the water after the river level drops. The sand prevents evaporation, key as climate change increases temperatures in the area increasing surface water evaporation, and acts as a filter, making the water safe for drinking.
The dams change life for communities. In Makueni County, southeast of Nairobi, for instance, Kiolo says during the dry season a woman may arise at 5:30 a.m. and walk two hours to the nearest river, fill her 20 liter jug and return. She rests briefly before taking her livestock for watering. Later that day, about 7 p.m., she gets in line at a river much closer. But the line is long and she may wait for two hours. Once her jug is full, she returns home for dinner, only to make one more trek during the night. The next day, she says, is spent sleeping to recover. In these villages, Kiolo says, children fetch water rather than attend school.
In one village, building a sand dam shortened the trek for water from nearly four miles to a little more than half a mile, saving time and improving sanitation and hygiene. The area near the dam also develops a micro-climate (like an oasis does), regenerating trees, shrubs and perennial herbs and encouraging family gardens.
The idea is spreading. The Sand Dam Foundation has partnered with other nonprofits to adopt the practice in Zimbabwe, Sudan, Uganda, Tanzania, Chad, Mali, Swaziland, and Mozambique.
"It’s innovative yet is a simple, replicable technology that traps rainwater where it falls, making water available all year round," Kiolo says.
Perhaps the most widespread use of rain harvesting techniques is in India, where groundwater levels are dropping rapidly. In the past few years, the state of Rajasthan, India's driest area where temperatures can reach 120 degrees, has turned to several techniques. In one, the paar, rainwater is collected in a catchment and flows into sandy soil. To access the water, residents dig wells about 15 feet deep.
In Rajasthan’s Alwar district after wells dried up, locals turned to johads, earthen dams that capture rainwater and recharge groundwater. After building more than 3,000 johads, groundwater tables rose nearly 18 feet and adjacent forest coverage increased by a third, according to one report. Five rivers that went dry after the monsoon season now run all year long. How important are the old techniques? The Confederation of Indian Industry (CII) in a Vision 2022 document for Rajasthan lists water harvesting as a vital focus. And a government master plan to recharge groundwater lists johads, paars and other traditional structures.
One of the driving forces behind the work in Rajastan has been Jethu Singh Bhati, who has worked with the Thar Integrated Social Development Society on indigenous ways to preserve water since the mid-1990s.
"Governments pride themselves on expensive projects," he told a reporter last year. "But our work shows that systems intrinsically linked to the region’s hydrography, topography and economy are most effective."