The Press Democrat reports that the owner of the truck linked to the cases has come forward.
However, investigators don't think that person is responsible.
They say it may have been the work of juveniles the owner allowed to borrow the truck.
There have been six confirmed instances of someone throwing water bottles at the windshields of moving cars along Highway 12 near Santa Rosa.
The name of the truck owner has not been released.
Officials say no one has been taken into custody.