Metropolitan explores Treated Water Augmentation to slash Pure Water pipeline costs

Metropolitan explores Treated Water Augmentation to slash Pure Water pipeline costsAs the Metropolitan Water District advances its Direct Potable Reuse plans, officials project that shifting to Treated Water Augmentation could reduce conveyance capital costs by up to 14%, though directors are pushing to eliminate new pipelines altogether.

Treated Water Augmentation (TWA) scenarios could reduce the required backbone pipeline diameter from 84 inches to 54 inches, cutting capital costs by 12% to 14% compared to baseline Raw Water Augmentation.

Director Desi Alvarez pushed staff to investigate a "no-pipe" solution that would inject purified water directly into the central pool via the Second Lower Feeder.

Metropolitan plans to seek board approval in early 2027 for a CM/GC contract to build a $72 million DPR demonstration facility.

Staff emphasized that TWA requires significant engineered buffering capacity, with existing sites like Garvey Reservoir requiring further study due to potential nitrification and capacity limits.

Metropolitan Water District (MWD) is evaluating Treated Water Augmentation (TWA) strategies for its Pure Water Southern California (PWSC) program to significantly reduce the footprint and cost of its conveyance infrastructure. During an August 12, 2026, caucus meeting at the West Basin Municipal Water District, MWD staff presented findings showing that TWA could cut pipeline capital costs by up to 14% compared to traditional Raw Water Augmentation (RWA). Under the baseline RWA scenario, purified water would be sent to drinking water treatment plants such as Weymouth and Diemer, requiring an 84-inch backbone pipeline. Alternatively, TWA scenarios would deliver advanced treated water directly into MWD's treated water feeders, such as the Second Lower Feeder or Middle Feeder. Staff noted this approach would allow the agency to downsize the majority of the pipeline to 54 inches, reducing overall lifecycle costs by 3% to 10%. Despite the projected savings, the presentation faced pushback from Director Desi Alvarez, who urged staff to prioritize a "no-pipe" solution. Alvarez advocated for treating the water to Direct Potable Reuse (DPR) standards at the Advanced Water Purification Facility in Carson and injecting it directly into the central pool, thereby avoiding the massive capital costs associated with new pipelines and satellite treatment facilities. "Why do we keep coming back to building the pipelines when we can do treatment... and go for direct potable reuse into the central pool?" Alvarez asked. MWD Water Resources Team Lead Matt Hacker and Program Manager Gloria Lai-Blüml acknowledged the economic appeal of a zero-pipeline option but cautioned that significant technical hurdles remain. Lai-Blüml noted that TWA requires substantial engineered buffer capacity for emergency response and operational flexibility. Existing infrastructure, such as the Garvey Reservoir and Palos Verdes Reservoir, are being evaluated as potential buffers, but pose challenges including potential nitrification issues and limited capacity. To validate the regulatory default and alternative treatment trains for DPR, MWD is advancing a $72 million demonstration facility at the Grace F. Napolitano Pure Water Southern California Innovation Center. Staff plans to seek board approval for a Construction Manager/General Contractor (CM/GC) agreement in early 2027, with testing slated to begin in 2029. Directors also highlighted the critical need for public acceptance. One board member warned that TWA will require a "massive outreach effort" before any final implementation decisions are made, prompting staff to confirm plans to incorporate tasting stations at the new demonstration facility to build public support.