BERKELEY, Calif. . Almost every number used to analyze California’s drought can be debated, but this can be safely said: No level of restrictions on residential use can solve the problem. The solution lies with agriculture, which consumes more than its fair share.

That doesn’t mean homeowners can’t and shouldn’t cut back.

But according to estimates by the Public Policy Institute of California, more water was used to grow almonds in 2013 than was used by all homes and businesses in San Francisco and Los Angeles put together. Even worse, most of those almonds are then exported . which means, effectively, that we are exporting water. Unless you’re the person or company making money off this deal, that’s just nuts.

California produces more than 400 commodities in many different climates, so it’s difficult to generalize about agriculture. Many farmers are cutting back on water use, planting geographically appropriate crops and shifting to techniques that make sense, like “dry” farming. Others, however, are mining water as they would copper: When it runs out, they’ll find new ways to make money.

So the big question is not, “How do we survive the drought?” . which could well be the new normal . but, “How do we allocate water sensibly?” California grows fruits and vegetables for everyone; that’s a good thing. It would be an even better thing, however, if some of that production shifted to places like Iowa, once a leading grower of produce. That could happen again, if federal policy subsidized such crops, rather than corn, on some of that ultra-fertile land.

California also grows alfalfa (which uses more water in total than any other crop . yes, more than almonds) that then gets shipped to China. It grows lettuce in the desert, and other crops in places that make no sense. The state has also become the biggest dairy producer in the country; at least a part of that industry would work better back east, where both water and land are available. That everyone in California needs to conserve water is a no-brainer. But a relatively small adjustment in agricultural use could make this drought look like a period of abundance. Properly managed, there is more than enough water for everything important. Improperly managed, as it has been for more than 100 years, there is a crisis.

It won’t be easy to rationalize water use in the face of powerful water-dependent interests; though agriculture is a surprisingly minuscule part of the state’s gross domestic product, it’s a big political force. But Gov. Jerry Brown and the State Water Resources Control Board have the authority to do what it takes, as the constitution says “waste or unreasonable use” are to be prevented.

The system is arcane, allowing some people and entities to get surface water nearly free. (This system, involving “senior,” as in inherited, water rights, has never been successfully challenged.) Others, sometimes including cities, can pay 100 times more.

In most areas, groundwater for landowners is “free,” as long as you can dig a well that’s deep enough. This has led to a race to the bottom: New, super-deep wells, usually drilled at great expense, are causing existing shallower wells, often owned by people with less money, to run dry.

That’s more than unfair: Groundwater that’s built up over a millennium is being removed too rapidly to be recharged, and in some cases the land is sinking as the water-saturated layers beneath it go dry. Those layers will most likely never be replenished, making this a form of environmental suicide.

Knowing this, Brown has announced mandatory cutbacks of an average of 25 percent in residential water use. He hasn’t said much about agriculture, but he must. He needs to see this crisis as an opportunity to rationalize the system.

Last September, Brown signed the state’s first bill to manage groundwater; the most important groundwater basins are due to be “in balance” . that is, recharged at a sustainable rate . by 2040. That’s probably too late.

It would be better to have a national policy preventing profit-making from public water and to encourage agriculture where it’s more naturally supported by the climate. But until that happens, Brown should challenge senior water rights, strictly regulate the pumping of groundwater, and perhaps even stop irrigation entirely on lands where growing water-intensive crops makes no sense.

When I arrived here a few months ago, an old friend who moved here in the 1980s came for dinner and scolded me for my dishwashing technique: “Turn that water off; there’s a drought.”

I almost pointed that my use of water was trivial compared with ... well, nearly everyone else’s. But I shut up. After all, every drop really does count. Wise use and conservation . not new dams, not desalination . are the answers, and conservation means common sense should take precedence over profiteering.