April 14 is a big day for the world of water.

That’s when the Metropolitan Water District in Los Angeles will decide whether to cut deliveries to cities throughout Southern California.

(Quick explainer: Metropolitan is the wholesaler that gets water from the Colorado River and the Sacramento-San Joaquin River Delta, our two main sources. It supplies much of Southern California with water, including the San Diego County Water Authority, the local wholesaler. The authority then sells water to local agencies from Fallbrook to San Diego. They, in turn, sell it to you.)

The authority is preparing for Metropolitan to make a 10-15 percent cut. That’s not as bad as had been feared. Earlier this winter, officials were projecting the cut could be as high as 30 percent.

The impact on local residents will differ greatly depending on whether Metropolitan cuts 10 percent or 15 percent.

Since the authority isn’t solely dependent on Metropolitan for water, a 15 percent cut gets diluted to be a 9-10 percent cut.

A 10 percent cut gets diluted to a 6-7 percent cut.

A seemingly inconsequential 3 percent difference. But for water managers, that’s a big gap.

Here’s why.

If a 10 percent cut is delivered, the region could possibly, maybe, potentially, perhaps reduce water use by 6 percent without mandatory water cuts. But residents haven’t proven they can get there. Urged to voluntarily conserve 10 percent last year, they saved 5 percent.

If a 15 percent cut comes, voluntary conservation is less likely to get a 9 percent to 10 percent reduction. There’s a better chance of mandatory restrictions in this scenario.

A debate is shaping up about what to do in either circumstance. Would residents voluntarily conserve 6 percent if they knew they’d face water-use restrictions otherwise? Would that bet be worth the risk for local water agencies who’d otherwise have to pay penalties to the authority if their customers didn’t meet the goal?

That discussion hasn’t been resolved.

Bob Yamada, the authority’s water resources manager, said the authority must weigh more factors than just the straight percentage reduction. The authority must decide how deeply to delve into storage to ameliorate cuts, knowing that pumping restrictions on the Sacramento-San Joaquin River Delta aren’t going away and could get tighter later this year.

Another factor: This winter was slightly drier than average, preventing statewide reservoirs from being refilled. “This is not just a single year event,” Yamada said.

“We’re at a tipping point with supplies, we’re on the edge,” Yamada said. “Because of the pumping restrictions and we’re still dry this year — those factors are combining to say we need to be prudent about how we use storage.”


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