While indirect potable reuse (IPR) has been used in southern California (USA) since the 1970s, the commissioning of the 265-megalitre-per-day Groundwater Replenishment System (GWRS) in Orange County (California) showed the region's commitment to utilizing reuse as a major source of potable water augmentation. The treatment process used at GWRS has become the benchmark on which California regulations were based and which other IPR facilities are measured against. As the cities of Los Angeles and San Diego move forward with their own IPR programs, they have commissioned pilot-scale and demonstration-scale projects to build on the lessons learned at the GWRS and to aid in developing future projects that are efficient, effective, and publicly supported. This paper will discuss the technical approaches being evaluated in these projects and the lessons learned in the operation of the existing full-scale facilities.

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