CA AB1944

Divides the San Luis Rey Valley Groundwater Basin (Basin 9-007) into Upper and Lower subbasins at the east line of Range 3 West, San Bernardino Meridian.

Designates both Upper and Lower San Luis Rey Valley Groundwater Subbasins as medium priority until the Department of Water Resources reassesses basin prioritization.

Requires groundwater sustainability agencies to include water beneath the surface within the Upper San Luis Rey Valley Groundwater Subbasin in their groundwater sustainability plans, with an exception for water downstream of the San Luis Rey River and Frey Creek confluence extracted under existing appropriative water rights.

Preserves all existing water rights and their priorities under state and federal law, and maintains the application of California's Water Code Division 2 to both subbasins.