How California water rights work, and why they are so contested
Two overlapping systems, both older than most of the state's infrastructure, allocate a resource that is now routinely oversubscribed.
California allocates surface water through two systems that developed separately and now coexist awkwardly.
Riparian
A riparian right attaches to land that borders a watercourse. It permits reasonable use on that land, does not depend on when it was first exercised, and is not lost by non-use. Riparian holders generally share shortage proportionally.
Appropriative
An appropriative right allows diversion for use away from the watercourse, and is ranked strictly by seniority. In shortage, the most senior right is satisfied first, and junior rights receive nothing rather than a reduced share.
Groundwater
Groundwater was historically pumped with little regulation, which is why some basins subsided measurably. The Sustainable Groundwater Management Act requires local agencies to bring designated basins into balance over a defined horizon through plans, monitoring and, where needed, pumping limits.
This is the largest change to California water in a generation, and its effects are landing now as allocations tighten in agricultural basins.
“The fights over groundwater are not about the science. They are about who reduces pumping first.”
Adjudication
Some basins have been adjudicated — a court has determined every holder's entitlement. Adjudicated basins are more predictable and vastly more expensive to establish.
Practical points
- Establish which right type attaches to a property before valuing it.
- In agricultural land, check the basin's SGMA status and its plan.
- Treat historic pumping levels as a starting point, not an entitlement.
