How many California cities produce too little housing? Almost all.

Thanks to SB35, state Sen. Scott Wiener’s important new housing streamlining legislation, we now know how many California cities and counties are behind on their housing development goals: nearly every single one of them. Every eight years, the state gives local governments targets for increasing housing production in line with population growth. Because there have been few penalties for local governments who fail to meet the goals, few were meeting them. According to the state Department of Housing and Community Development, 397 cities and counties are behind. That’s a whopping 97 percent of California’s cities.

“When 97 percent of cities are failing to meet their housing goals, it’s clear we need to change how we approach housing in California,” Wiener, D-San Francisco, said in a statement.

The state’s shocking numbers are a crucial first step, and they certainly show the depth of California’s current housing crisis.

But getting California’s local governments to build more housing won’t be easy.

One potential loophole in SB35 is the fact that it requires local governments to streamline certain kinds of housing production if it meets their own local zoning rules.

So an obvious concern is that local governments will simply change their zoning rules.

An incident in Cupertino late last year offers an instructive lesson in the battles to come.

Cupertino, which recently added an Apple campus for 12,000 workers with no additional housing, has been deeply divided over redevelopment plans for a huge, nearly derelict 1970s-era shopping mall known as Vallco for years.

The developer’s plans to move forward with a project including hundreds of new homes and millions of square feet of office space have been the subject of not one but two local ballot measures.

The measures’ results weren’t definitive about what residents want. (The site’s developers initiated a new series of public input meetings this month.)

Nevertheless, in November, a couple of City Council members called for a study of ways to prevent the huge project from being subject to the state’s new requirement, possibly through changes to Cupertino’s planning codes.

After an outcry, Cupertino city officials denied trying to change the city’s planning regulations to avoid building housing at the site.

But if they were tempted to do so, other local governments will be, too.

Because the state attorney general can now go after local governments that are flagrantly out of compliance with their housing requirements, communities won’t be able to just downsize their way out of meeting their responsibilities.

But SB35 still has loopholes, and history has shown how passionate Californians can be about preventing home production.

Local governments still have to do the right thing for the future of California.