Safe storage of water? Go underground.

Wise usage Experts are stressing the importance of building reservoirs below the ground. This will solve many of the difficulties associated with above-ground water shortage. Proponents say that the technology will only become more relevant with climate change.

When cities store water for future use, they often use large lakes created by damming rivers. Now, experts are urging cities to build reservoirs below the ground, where the water cannot evaporate and many of the difficulties associated with above-ground water storage are avoided. “It just makes so much more sense,” said Jim Lester, president of the Houston Advanced Research Center, a nonprofit research group. Among other advantages, he said, underground reservoirs are less expensive to build than their above-ground counterparts. Australia and the United States have increasingly embraced underground reservoir technology. Among European countries, Belgium and the Netherlands developed systems of storing water in sand dunes decades ago. The water utility that supplies London, Thames Water, stores surplus treated water in a chalk aquifer beneath northeast London, a project that the company expanded after a 2006 drought.

Improving water security

Underground reservoirs could help improve water security in the Middle East, according to Thomas Missimer, a visiting professor of environmental science and engineering at the King Abdullah University of Science and Technology in Jidda. Abu Dhabi is working on two such water-storage systems, he said, one in sand dunes, and the other in a type of alluvial plain. “Locating the right aquifer to achieve what you want is the key,” Missimer said. The idea of storing water in the earth is not new. Long ago, the Bedouins blocked ravines with large stones, backed by sand. Water collected in the sand could be extricated by digging, according to Missimer, who has co-written a book on underground water storage technology.

Old technique

In the modern world, the United States began using the technology around the 1960s. Typically, water is injected into an aquifer, stored and then pumped back up to the surface for disinfection and use. The technique has the formal and somewhat cumbersome name ‘aquifer storage and recovery’. Its advantages are myriad, supporters say. Storing water underground averts the need to flood land above ground, a contentious and potentially litigious process. “You don’t flood a bunch of bottomland hardwoods, or take thousands and thousands of acres of cropland out of service,” said James Dwyer, an engineer with a global engineering and construction company.

Compared with above-ground reservoirs, “the space in the sub-surface is simply much, much greater, and you don’t need to build walls,” Theo Olsthoorn, a professor of groundwater hydrology at the Delft University of Technology in the Netherlands, said. In addition to the dune projects, he said, some farmers in western parts of the Netherlands collect rainwater from the roofs of their greenhouses during the autumn and winter, inject it into a well for storage and retrieve it during the growing season, he said.
Storing water underground also may reduce the need to dam up rivers, and avoids losing water to evaporation.

Evaporation can be such a problem that some reservoirs in arid areas of the world, including western Texas, lose more water each year into the air than people actually use. The aquifer itself can also serve as something of a natural cleanser, according to Missimer. This especially helps in instances in which water utilities store treated wastewater in the ground, as happens in El Paso, Texas, for example.

But not every aquifer is well-suited to the technology. Florida, where underground reservoir technology has been used for several decades, faced some early struggles with arsenic in the water, and other challenges as well. “It’s been a learning process,” said Bob Verrastro, the lead hydrologist with the South Florida Water Management District, which has financed several projects that use the technology. Florida utilities like the idea because demand for water is seasonal: Americans flock to Florida in the winter, but it rains the hardest in the summer. So, storage is important. Not every aquifer is suited to the technology. Aquifers ideally have a certain level of salinity. That allows the fresh water that is being stored to rest atop the displaced saline water and be readily accessible.
Yet to be accepted

Wells can occasionally clog, as happened during a trial in Adelaide, Australia, in 1997, in which storm water was injected into an aquifer. Another challenge is legal. Utilities injecting water into an aquifer must make sure the water is legally theirs to recover. In Texas, for example, ‘rule of capture’ law means that anyone has a right to recover water under that person’s land. So, even if a utility injected the water, in theory it could belong to someone else, once it emerged through a well.

Lester, of the Houston research group, said that the main reason the technology was underused was education. Water utilities, he said, typically do not understand that the underground reservoir technology is already tested and ready to go.

Proponents say that the technology will only become more relevant with climate change.
Water from melting glaciers in places like Chile, China, India, Pakistan and Peru could be stored underground, Missimer said. In addition, more extreme weather, like drought and flooding, is expected in the future. “With these flash floods, we need to try to capture, and take some of that water and store it in the ground,” Missimer said.