6.1 Purchased or Imported Water
Imported Potable Water
Approximately 33% of IRWD’s potable water needs are met by imported water purchased and supplied by Metropolitan through MWDOC. IRWD receives imported potable water supplies from the Colorado River and the State Water Project (SWP) through Metropolitan’s Diemer Filtration Plant and Weymouth Treatment Plant. The majority of IRWD's imported potable water is supplied from the Metropolitan Diemer Filtration Plant, located north of Yorba Linda. Typically, the Diemer Filtration Plant receives a blend of Colorado River water from Lake Mathews. The blend ratio between the Colorado River and SWP sources varies seasonally and from year to year. Diemer Filtration Plant treated supplies are delivered through the Allen McColloch Pipeline (AMP) and East Orange County Feeder #2 (EOCF#2) pipelines. Weymouth Treatment Plant treated water is delivered primarily through the Orange County Feeder (OCF) and Coastal Supply Line (CSL). IRWD owns 64.7 cubic feet per second (cfs) capacity in the AMP, 41.4 cfs capacity in all reaches of the EOCF #2 down to Coastal Junction, and 18 cfs in the OCF.
Imported Non-Potable Water
IRWD purchases untreated imported water supplied by Metropolitan through MWDOC. Untreated imported Colorado River water from Lake Mathews is supplied to the Baker Water Treatment Plant (Baker WTP, Baker). Starting in 2027, IRWD will begin treating up to 4 million gallons per day (mgd) of water from Lake Mathews in the Howiler Treatment (Howiler WTP) for delivery into IRWD’s service area and by agreement when requested in the Serrano Water District. The Baker WTP, completed in 2016, is a 28.1 mgd drinking water treatment plant. It was constructed as a joint regional project that serves treated water to IRWD and four other water agencies. IRWD also uses untreated imported water to meet certain agricultural and irrigation demands that cannot otherwise be met with recycled water, and to supplement IRWD’s recycled water system during peak months. Imported untreated Colorado River water from Metropolitan’s Santiago Lateral is delivered to IRWD through the OC-33 turnout connection, which directly supplies to Irvine Lake, the Baker Pipeline, and ultimately the Baker WTP and the Howiler WTP. The Baker Pipeline, formally known as the Santiago Aqueduct or SAC Pipeline provides untreated imported Colorado River water. IRWD’s original owned capacities in the Baker Pipeline include 52.70 cfs in the first reach, 12.50 cfs in the second, third and fourth reaches and 7.51 cfs in the fifth reach of the pipeline. IRWD’s original Baker Pipeline capacities have been apportioned to the Baker participants based on Baker capacity ownership. IRWD retains 10.5 cfs of the pipeline capacity for its Baker WTP capacities and retains 36 cfs in first reach of the pipeline for non-potable supply. Later in this Section, DWR Table 6-8 and DWR Table 6-9 show IRWD’s current and projected purchased supplies (potable and non-potable) for 2025 and through 2045. The volumes shown in DWR Table 6-9 do not represent IRWD’s total connected delivery capacity through Metropolitan and MWDOC but rather are based on average connected capacity. IRWD’s
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IRWD – 2025 Urban Water Management Plan
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