Purple Pipe to Potable: A Case Study

Presentation Description: California led the nation when adopting regulations for the use of recycled water to irrigate crops in 1918, and has invested aggressively in non-potable reuse over the last century. Potable reuse, however, is on the rise. The Los Angeles Groundwater Replenishment Project (LAGWR) discussed here is only the first of several potable reuse projects on the horizon in Los Angeles, including OpNEXT and PureWater SoCal. DPR regulations finalized by the State Water Board in 2023 have further widened the field of reuse.
Utilities throughout the state are at a decision point regarding the application of their recycled water: purple pipe, or potable? The Los Angeles Department of Water & Power (LADWP) and Los Angeles Sanitation (LASAN) are navigating the balance between NPR and IPR while delivering LAGWR with consultant Jacobs. Without further adjustment, LAGWR would feed IPR quality water into the same pipelines that still supply legacy NPR customers. Unnecessarily providing IPR grade water for NPR use would introduce avoidable energy and chemical expenditures. The goal is therefore to provide water at a quality that is fit for purpose, where feasible.
LAGWR feeds into a recycled water conveyance system that allows isolation of local (Sepulveda Basin) NPR demand with minimal re-plumbing. This allows 1.4 MGD, or roughly half, of the total NPR demand to remain on chlorinated tertiary effluent. The cost savings generated by avoiding additional treatment of this water (electrical, chemical, and maintenance) in LAGWR’s Advanced Water Purification Facility will be explored in this presentation. This case study reinforces the need for utilities to design NPR distribution systems with enough flexibility to accommodate a possible transition to potable reuse in the future, and the financial case for matching the quality of water provided to its intended application.
Understanding and engaging with the community has been beneficial to both LADWP and its rate-payers. By meeting with customers and understanding their infrastructure LADWP, LASAN and Jacobs were ultimately able to down-size pumps for the newly isolated line, reducing the capital and operational cost associated with NPR delivery. These savings will be passed directly on to the rate-paying citizens of Los Angeles.

.1 SWRCB Education Units
1 SWRCB Drinking Water Contact Hour