The climate crisis has placed a strain on California's already limited water resources, with the state projected to lose 10% of water its supply by 2040. Persistent scarcity is compelling California to adopt advanced water recycling regulations that transform wastewater into tap water.
In October, California introduced rules for direct potable reuse, or DPR, which transforms municipal wastewater—a mix of sewage and stormwater runoff—into drinking water for residential and commercial use.
Proponents call the new regulations a “gamechanger” for a state reeling from natural disasters, intensifying climate change and contaminated water supplies. Through direct potable reuse, communities and water agencies can expand water resources while protecting their existing supplies, noted Sunny Wang, water manager for the city of Santa Monica.
“The process is climate resilient and a source that gives us more flexibility, especially when there are years when we’ll have less imported water,” said Wang. “It’s like an investment portfolio with high- and low-risk stocks. Imported water is more variable, while we can always count on this new supply to be there.”
Prior to the recent regulations, California permitted only indirect potable reuse. In this process, highly treated wastewater is introduced into an aquifer, where it undergoes additional natural filtration. Direct potable reuse bypasses groundwater injection, instead delivering treated wastewater straight to treatment facilities for further processing.
Ideally, direct reuse can offset impact of decreased water supplies from the Colorado River, a victim of the ongoing drought plaguing western states. Climate change has also diminished the once-reliable Sierra Nevada snowpack, leading to accelerated evaporation along with absorbed runoff by wildfire-scorched landscapes, said Wang.
“When the snowpack melts, it may just evaporate quickly, so the water isn’t making it into surface reservoirs,” he said. “When there are fires, the ground just absorbs the water.”
Putting Pieces in Place
Southern California has employed water recycling techniques to irrigate its landscapes for decades. Nor is recycling drinking water a novel concept for the Sunshine State—Orange County has been turning raw sewage into drinkable water since the mid-2010s through microfiltration, reverse osmosis and blasts of ultraviolet light.
Direct potable reuse would put recycled water directly into community water systems, a boon for cities like Santa Monica that don’t have enough space in groundwater basins due to past pollution, said Wang.
Cost is another obstacle to water recycling for many communities. A single injection well—utilized to introduce wastewater into porous rock formations deep underground—cost Santa Monica upwards of $6 million. Although the city boasts one of the world's most advanced water recycling facilities, it seeks to implement direct potable reuse within three to five years.
“The treatment process to meet regulations isn’t as big of a challenge for us, because we already have the pieces in place between our advanced water treatment facility on the water recycling facility side, and our groundwater remediation facility on the drinking water side,” Wang said.
About 250 million gallons of L.A. County's wastewater is partially treated and released into the ocean. The new project aims to recycle this water to drinkable standards, said Darrin Polhemus, deputy director for the division of drinking water with the California State Water Resources Control Board.
“Nobody can count on one water supply anymore, because those will be unreliable in some circumstances,” said Polhemus. “Switching among sources is key.”
Polhemus envisions California cities turning to the system in years of high drought, either regionally or from import sources like the Colorado River, which has been stretched thin by the worst “megadrought” in 1,200 years.
Direct potable reuse will likely account for 5%-15% of a participating municipality’s water supply early on. Coming decades may find bigger cities harnessing the system at a higher rate—perhaps 35%-40% of total supply—depending on plant infrastructure and other factors.
“In the short-term, it’s about building up the human infrastructure as well,” Polhemus said. “Cities are pursuing this work step by step from indirect potable reuse to DPR to build up the experience of their core people. It will take a high level of expertise to manage these systems appropriately.”
Answering Safety Concerns
Some residents are understandably skeptical about drinking recycled wastewater, yet this type of water recycling is the most stringent in the nation. Even stormwater has more contaminants than wastewater—oil, grease, heavy metals and more, said Wang, the Santa Monica official.
Wang points to Orange County’s three-tier recycling system as something that could translate to the remainder of the state.
“Those three technologies mean there are strict regulations when bringing this water directly into the home,” Wang said. “There’s been lots of research on what level of treatment is necessary to ensure the protection of public health. The evaluation process is a gamechanger.”
As for billing, California ratepayers may see increases depending on factors like the upfront infrastructure costs for a new system. Drought rates could play a factor as well, although about 65%-70% of California water costs are fixed, said Wang.
Long-term challenges include added precision in water treatment, as recycled water will be distributed more rapidly. However, the potentially transformative benefits of direct potable reuse make these obstacles worthwhile, Wang said.
“There will be operational requirements for the monitoring and staffing needed for direct potable reuse, when compared to either drinking water treatment or more traditional water recycling operations,” he said. “But this system will let us add another source to our portfolio.”
