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More than two-thirds of Saudi Arabia's irrigation water and a third of the country's drinking water comes from groundwater, yet aquifers are being depleted faster than they recharge. At the same time, sewage treatment generates large volumes of treated wastewater: 1.6 billion cubic meters of treated wastewater is underutilized throughout the country each year, says Mohammed Benaafi, a research scientist at King Fahd University of Petroleum and Minerals.

That wastewater is equivalent to about 60% of Saudi Arabia's annual urban drinking water demand, he says. This overlooked water resource could help stabilize water supplies in one of the world's most water-stressed regions. "It is a strategic asset that could be utilized for aquifer recharge."

Using laboratory experiments , Benaafi and his colleagues tested whether treated wastewater can safely recharge coastal aquifers under realistic managed aquifer recharge conditions.…