Nothing is more important to California than its water supply. Yet Gov. Jerry Brown and the Legislature are playing Russian roulette with one of the state’s most precious resources.

The primitive conditions of the levees guarding the Sacramento-San Joaquin River Delta are shocking. The Delta is mostly below sea level. It provides water to 65 percent of Californians, including more than half of Silicon Valley, and those fragile levees are the only thing preventing salt water from San Francisco Bay from spoiling the fresh water flowing from the rivers.

Hundreds of miles of levees were built out of sand and dirt by immigrants, wheelbarrow by wheelbarrow load, in the late 1800s and early 1900s. Saying they’re primitive is kind. They are at extreme risk of collapsing in an earthquake or flood. State Sen. Joe Simitian, D-Palo Alto, calls them “California’s Katrina waiting to happen.”

But neither Brown nor the Legislature has even tried to expedite repairing the levees. Last week, the state ballot proposition for an $11 billion water bond was postponed again, this time until 2014. That’s fine because we can’t imagine that porker passing anyway, but the $1 billion in absolutely necessary repairs to the levees should have been done years ago.

Brown and lawmakers are holding the levees hostage to help persuade voters to approve a peripheral canal (or tunnel, depending on whom you talk to) around the Delta to feed Southern Californians and Big Ag an even higher percentage of the water. Expect that grand plan to be unveiled July 25. But don’t expect wild celebration in these parts. Nobody knows for certain how it will affect the ecological health of the estuary, let alone how much it would cost or where the money would come from. Of course, Southern California has made verbal commitments to do its part. Whatever that means.

Since 1900, more than 150 separate levees around the Delta have failed, and thousands of acres of onetime farmland has been permanently flooded. In 2004, on a sunny June day, “one of the best levees in the Delta” inexplicably and without warning collapsed, creating a 200-foot break. Within hours, water swamped more than 12,000 acres and nearly took out Highway 4 between Tracy and Antioch.

Besides flood damage, failed levees can mean water is not available for pumping — or can cause salt water to move up from the bay. If that type of levee break happened closer to the bay, bringing the salt water close to pumping stations, it could be catastrophic to Silicon Valley’s water supply.

We need the levees shored up first, protecting the water supply we’ve got. When water is soaking into farms and swamping highways, it’s not going to anybody’s faucet.

Then let science dictate how best to meet the state’s water needs while ensuring the environmental health of the huge estuary we so heavily rely on.