Groundwater basin adjudication occurs when a groundwater user or a class of users files an action asking a court to establish groundwater rights. Generally this occurs when a groundwater basin is in overdraft . In basins where a lawsuit is brought to adjudicate the basin, the groundwater rights of all the overliers and appropriators are determined by the court. The court also decides:
- Who the extractors are;
- How much groundwater those extractors can extract; and
- Who will serve as the Watermaster to ensure that the basin is managed in accordance with the court's decree. The Watermaster must report periodically to the court.
Adjudication in San Luis Obispo County
There are two groundwater basins in adjudication in San Luis Obispo County: the Los Osos Groundwater Basin and the Santa Maria Groundwater Basin.
There are 22 adjudicated groundwater basins in California.