Compared with above-ground reservoirs, “the space in the subsurface 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 an e-mail.

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 fall 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 Mr. Missimer. This especially helps in instances in which water utilities store treated wastewater in the ground, as happens in El Paso, Texas, for example.

However, 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.