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SAN DIEGO – In a historic consensus, California, alongside the six other states that rely on the Colorado River for survival, announced an agreement last week for a plan to cut back water usage over the next three years.

The proposal drafted by the three lower basin states – California, Arizona and Nevada – would cut water use from the river by at least 3 million acre-feet by the end of 2026 through conservation to prevent the river’s reservoirs from falling to critically low levels. 

Of that total, 1.5 million acre-feet at minimum will be conserved by the end of next year under the proposal. One acre-foot of water supplies enough water for about 2.5 households of four people per year.

While the proposal has not yet been approved by federal regulators, San Diego County residents might already be asking themselves whether this crucial, statewide conservation effort might impact their household water supply. 

But, the San Diego County Water Authority (SDCWA) Colorado River Program Manager Alexi Schnell says that it’s not likely.

As she explained, that’s because, while the region relies on water from the Colorado River, most of what flows into San Diego homes from the river is not coming directly from the source, due to years-long concerted efforts by the region’s water authorities to diversify the county’s hydrology.

Each basin is allocated about 7.5 million acre-feet of water from the river, totalling 15 million acre-feet of water. California, the state that uses the largest share of the supply, receives an estimated 4.4 million acre-feet annually. 

In the early 2000s, California was consistently using more than their annual entitlement, prompting local water authorities in Southern California to propose the Quantification Settlement Agreement (QSA).

The agreement, signed in 2003, laid out rights to portions of the Colorado River supplies for the Southern California water authorities: SDCWA, the Imperial Irrigation District, the Metropolitan Water District and the Coachella Valley Water District.

The QSA established a 75-year agricultural to urban water transfer from farmers in Imperial Valley, who are the biggest users of the Colorado River, to reduce reliance on direct imports. It has since become the largest transfer system of its kind in the country.

State funding was also made available with the QSA for efforts to line portions of two major canals in the region – the All-American and Coachella canals – with concrete to reduce seepage and increase usable supplies.

Under the agreement, about 200,000 acre-feet per year are sent to the SDCWA, creating an independent supply from the Colorado River. An additional 77,000 acre-feet comes from reserves with the canal lining.

According to Schell, these two sources account for more than a half of the county’s water portfolio. Only about 13% of the water used by the county comes directly from the river through the Metropolitan Water District.

“We consider it the major cornerstone of the region’s diversified supply portfolio. We rely on making sure that we’re not dependent on any one source,” Schnell said. “The Colorado River plays into that very highly … (but) we’re not actually taking water out of the river.”

Because of that, she explained that San Diegans would likely see minimal change under the new agreement should it get federal approval, as the county already prioritizes conservation.

“The proposed plan doesn’t reduce San Diego supplies from the river, it uses conservation to achieve that savings,” Schnell said. “San Diego has always been great about conserving and conservation efforts. It’s a way of life here for San Diegans.”

However, the Imperial Irrigation District, the source of San Diego’s water via the QSA transfers, announced last week that it will reduce usage by roughly 250,000 acre-feet per year in exchange for the proposed federal funding from the Inflation Reduction Act. 

It’s unclear how reductions to the Imperial Irrigation District’s supply might impact the water transfers coming to San Diego.

In the coming months, Schnell said that the district will be exploring additional measures to ensure the region’s Colorado River supply, as well as further aid with federal and state efforts to help with the river’s long-term protection.

“(We’re) looking for possibilities as we work on the future of the river and all the collaborative efforts going into how to better manage the river in the future,” she explained, “certainly giving thought to how we could potentially use our supplies or coordinating to keep water in the river to help other parts of the Colorado River Basin, as well as the state.”