The Los Angeles–based Metropolitan Water District of Southern California owes the San Diego County Water Authority nearly $232 million, a San Francisco federal judge ruled Friday afternoon (October 9).

The San Diego agency had already been awarded $188.3 million in an August judgment stemming from a finding that Metropolitan had been overcharging for imported water from 2011 to 2014. Judge Curtis Karnow tacked on another $43.4 million in interest, bringing the total owed to $231.7 million.

Karnow threw out all of Metropolitan's arguments, including one asserting that the Authority had elected to voluntarily pay illegal rates (state law prohibits public water agencies from charging customers more than the actual cost of delivering services). The judgment represents another defeat for Metropolitan, which argued it should only pay $4.1 million in interest rather than the 10 percent awarded to the Authority.

"[Metropolitan] has dragged out this case for years, and the price tag for its illegal rates and failed litigation strategy continues to grow," said Mark Weston, chair of the Authority’s board of directors in an October 10 release. "This ruling should serve as another strong signal to MWD that its current rate structure is illegal and should be immediately reformed to comply with state law and the California Constitution. The rulings have been clear and decisive. It is time to fix the rate structure and avoid more unnecessary litigation costs to water ratepayers."

Metropolitan has promised to appeal and has 60 days to do so. If the decision stands, the Authority says it intends to refund its customers — local water districts — based on the proportion of overcharges they were forced to pay.

San Diego continues to import the majority of its water, including supplies purchased from the Imperial Valley, on Metropolitan's infrastructure. An estimated 57 percent of the region's overall supply this year will come in from out of the area.