Step 1: Visual check of markings (basic verification)
Examine the filter cartridge itself; most compliant products feature a clearly printed water flow arrow (→). This arrow indicates the direction of water outflow and must be perfectly aligned with the flow direction marked on the filter housing.
Some models use English labels: the end marked "IN" is the inlet and should face the tap water supply side, while the end marked "OUT" is the outlet and should face the showerhead side.
If the markings are worn or illegible, compare the new cartridge directly with the old one. Ensure the text and arrow orientation on the new cartridge match the installed position of the old one to replicate the correct orientation.
Step 2: Structural alignment check (physical error prevention)
Observe the structure at both ends of the cartridge; most shower filter cartridges feature an asymmetrical design. The end with positioning bumps or locking tabs must align with the corresponding grooves inside the filter housing; a "click" sound indicates it has locked into place, whereas installing it backward makes it impossible to push the cartridge fully home.
For cartridges with different-sized sealing rings at each end, align the end with the thicker rubber ring to the inlet side and the end with the thinner ring to the outlet side. Forced reverse installation would cause the rubber ring to twist or fail to seat properly in the groove, making it physically impossible to install correctly.
For special cartridges that are hollow at one end and solid at the other, the hollow end (with a through-hole) is the inlet and must align with the filter's water inlet; the sealed, solid end is the outlet and should face the showerhead. Installing this type backward will result in abnormal water pressure differentials.
