A California tunnel could save stormwater for millions.

Even after storms drenched the drought-parched Golden State, a plan to capture more water and send it southward remains controversial

As drought-weary Californians watched trillions of gallons of runoff wash into the Pacific Ocean during recent storms, it underscored a nagging question: Why can’t we save more of that water for not-so-rainy days to come?

But even the rare opportunity to stock up on the precious resource isn’t proving enough to unite a state divided on a contentious idea to siphon water from the north and tunnel it southward, an attempt to combat the Southwest’s worst drought in more than a millennium. The California Department of Water Resources said such a tunnel could have captured a year’s supply of water for more than 2 million people.

“People are naturally focused on, are we doing everything we can to capture the water when we can?” said Karla Nemeth, the agency’s director.

The proposal from Gov. Gavin Newsom’s administration — one that would cost $16 billion to help 27 million water customers in central and southern California — is spurring fresh outrage from communities that have fended off similar plans over four decades, including suggestions to build other tunnels or a massive canal. Before and since storms in December and January, there have been packed town halls and stern pleas to the Democratic governor from those for and against the idea. The appeals have come from state and federal lawmakers, including one pushing legislation in Congress to block the tunnel from receiving a key permit.

The conflict underscores the increasing difficulty of keeping taps running in communities far from the sources of the water they drink, and underlines thorny questions about the consequences of taking water from one place and giving it to another. There are concerns the tunnel would hurt farmers while failing to solve California’s larger water woes, stoking long-simmering state divisions: north versus south, inland versus coast, agricultural versus urban. Nevertheless, the water crisis demands solutions.

California faces a future climate marked by both extended drought and increasingly intense rainstorms, known as atmospheric rivers, like the ones that repeatedly lashed the state in late December and January. Warming temperatures and dry conditions mean snowpack isn’t translating to as much river flow as it once did, and at the same time, the West is struggling to develop a plan to sustainably drink from the dwindling Colorado River, another key source of water there.

To be built, the idea would have to withstand a long vetting process and any expected legal challenges. Even then, the tunnel likely wouldn’t be functional until maybe 2040. But the future of what would be one of California’s largest infrastructure investments ever could come to a head much sooner. Nemeth expects to decide whether and how to proceed by the end of the year.

A thirsty state, divided

It’s one piece of a larger strategy to “modernize” California’s water systems, Nemeth said. Other efforts aim to improve efficiency, promote reuse, adapt to a warming climate and prepare for damaging earthquakes, which the Army Corps of Engineers has said could damage levees that protect the water supply.