A water purifying filter assembly including a filter case including a receiving member having a protrusion; and a head assembly. The protrusion may be configured to be receivable in a recessed portion on an outer circumferential surface of a filter so that when the filter is placed in the receiving member with the protrusion received in the recessed portion, the filter is fixedly couplable to the head assembly by rotation of the filter, and when the filter is placed in the receiving member with the protrusion not received in the recessed portion, the filter is prevented from being fixedly couplable to the head assembly.

Keyed fluid-handling devices comprise a fluid-handling device such as a filter, a bypass, or an adapter and an optical key. The optical keys are amenable to all types of filter component and can be readily retrofitted to existing designs. The optical keys may be formed from a variety of materials and combination of phases. That is, optical keys may comprise one or more solid materials, or perhaps may result from a combination of: solid materials, such as in transparent or semi-transparent polymers or glass; liquid fluids, such as water; and gaseous gaps such as an air gap. Optical keys may be light conduits or light guides. Filter manifolds comprise optical locks to ensure compatibility of the filter components.

A housing module of a fluid treatment module of a fluid system is provided with a fluid housing with inlet and outlet for fluid. The fluid housing has a housing part with a receiving chamber for a fluid treatment component for treatment of fluid and an installation opening, closable by a housing closure part, for installation of the fluid treatment component in the receiving chamber. A housing connecting section is provided for connecting the housing part and the housing closure part to each other. The housing module has an externally positioned support structure that surrounds the housing part like a sleeve and has a reinforcement region that extends about the housing connecting section. The support structure has a fastening region for attachment of the housing module on a holding component of the fluid system. The connection of the housing part with the housing closure part is a direct connection.

A housing module of a fluid treatment module of a fluid system is provided with a fluid housing with inlet and outlet for fluid. The fluid housing has a housing part with a receiving chamber for a fluid treatment component for treatment of fluid and an installation opening, closable by a housing closure part, for installation of the fluid treatment component in the receiving chamber. A housing connecting section is provided for connecting the housing part and the housing closure part to each other. The housing module has an externally positioned support structure that surrounds the housing part like a sleeve and has a reinforcement region that extends about the housing connecting section. The support structure has a fastening region for attachment of the housing module on a holding component of the fluid system. The connection of the housing part with the housing closure part is a direct connection.