A locking liquid filter assembly is disclosed that prevents an unauthorized user from removing the filter media cartridge after installation. The locking filter assembly includes a head unit for coupling with an inlet conduit for delivering unfiltered process liquid into the filter assembly and an outlet conduit for delivering filtered process liquid from the filter, a head portion that includes a manifold for communicating with the inlet conduit and with the outlet conduit, and a locking assembly coupled to the head portion configured such that when the filter media cartridge is fully engaged with the head portion, the locking assembly engages with the filter media cartridge to prevent filter media removal.