If you thought California’s water wars were bitter, just wait until you see our water data wars.

Digital tools have expanded the ability of governments, companies and nonprofits to measure the uses of California water, and thus build more water-efficient products, boost water conservation, and replace expensive and inefficient infrastructure.

But the abundance of water data effectively makes every piece of land and every drop of water in California the subject of measurement—and conflict. The data also exposes the fragmentation and deficiencies of California’s system of water management.

The state’s new conservation requirements add to the stakes of the arguments over data. As Californians struggled to save every drop of water during the recent five-year drought, the state for the first time imposed mandatory restrictions on water use—requiring that 400 local water agencies figure out how to reduce usage by 25 percent in 2015. That shift, following 2009 legislation setting a goal of reducing urban per capita water use by 20 percent by 2020, is changing the way Californians fight over water—away from historic battles over dams, and toward new battles over maximizing the water we already have.

Among the questions to which new data is being applied: What incentives will convince most people to remove their grass lawns and, if they do, how much water do those removals save? How much water do efficient toilets and appliances really save? Exactly how much water are we losing to leaks—and where can we make the most efficient investments to stop them?

Then there’s a bigger-picture quandary: can data help integrate our water use with our electricity and gas use—making ourselves so efficient that we effectively mitigate the effects of climate change?

That promising thought is mixed with real questions about the accuracy of the data we do have. How precisely are we measuring, for example, evapotranspiration—the process by which water is transferred from the land to the atmosphere both by evaporation from soil and by transpiration from plants? And how accurately are we measuring our land—in terms of how much has landscaping on it—to determine how much could be replaced by more water-efficient plantings?

This is not easy work. When a state pilot project tried to measure landscape, it found that among 20 water agencies, there was no consensus on defining landscape areas or how to calculate them. Similar questions worm through other data, both at local and state level.

These issues are not petty—they are questions of justice. How much water savings can we demand from farmworker housing that draws on groundwater in the fields? Or how do you measure the right use of water on a large public park with multiple water meters?

In this context, the highly publicized controversy over the California Water Fix—Gov. Jerry’s Brown proposal to build tunnels under the Delta to convey water to the San Joaquin Valley and Southern California—feels like an anachronistic repeat of decades-old dramas about dams and peripheral canals. The more important fight today is over who controls the data and what it justifies.

This newer fight has lately involved legislation—SB 606 and AB 1668—that seeks to establish a management regime to realize the governor’s framework for “making water conservation a California way of life.” Much of the energy of the fight is over bureaucratic control—what powers will the state have to set standards, and what powers will be left to regional or local agencies? But questions over data  shadow every piece of the bills.

Younger, tech-savvy water players say that much of the data undergirding California water use is old or faulty. In an open letter to Governor Brown this summer, Patrick Atwater of the L.A.-based nonprofit ARGO wrote that state water agencies don’t have accurate land use information, don’t have landscape area definitions, and don’t have accurate service area boundaries for local water retailers.

There is an urgent need to modernize how California’s water agencies manage data,” he wrote, adding, “Achieving the broader urban water efficiencies will require creativity and finesse, not simply command and control regulation.” ARGO called for a one-year task force to focus on developing better-quality data and designing a 21st-century system of water governance, with more local control and management.

Such a transformation would be welcome. But it may be a long way off. For now, more data means more water wars.

Joe Mathews writes the Connecting California column for Zócalo Public Square.