High rates of water conservation helped California manage limited supplies during the 2012–16 drought. But conservation can have a downside. New research shows that indoor water conservation can reduce the quality and quantity of wastewater, making it harder for local agencies to use treated wastewater to augment their water supply.
We talked to two members of the research team about their findings: David Jassby, associate professor of civil and environmental engineering at UCLA; and Kurt Schwabe, professor of environmental economics and policy at UC Riverside and an adjunct fellow at the PPIC Water Policy Center.
Jassby summarized the problem: “In general, as people conserve water inside their homes, the concentration of contaminants in the wastewater goes up—organic matter, nitrogen, detergents, and more. All of these things have to be treated.”
Schwabe noted that in the past, recycled water was mostly used for irrigating nearby cropland and median strips—not drinking. But as treatment processes have improved and demand for water increased, recycled water has become an integral part of the drinking water supply in some areas, where it is used to replenish groundwater basins. In many communities, treated wastewater is discharged into rivers and streams and used by downstream entities that treat the water again.
Salinity is a particular challenge. “Most wastewater treatment plants can treat higher levels of nutrients, but they’re not designed to treat higher levels of salinity,” Schwabe said. “What this means is the water that is discharged into streams or to farms or into aquifers for groundwater recharge will be saltier, which reduces water quality and crop yields.”