A new correctly sized filter should maintain usable shower flow. Noticeable pressure loss after weeks or months often points to cartridge loading or scale rather than the filter concept itself.
Flow rate is not the same as pressure
A showerhead can feel weak because of low supply pressure, restricted flow, clogged screens or a loaded filter. Diagnose the actual restriction before replacing the entire system.
Cartridge loading
Sediment, scale and media fouling increase resistance over time. If flow improves immediately after cartridge replacement, the old filter was likely loaded.
Shower-specific evidence matters
Weddell publishes shower-specific flow and treatment data; that is more relevant than lab data collected at a slow drinking-water flow rate.
Hard water can mimic filter restriction
Scale in the showerhead nozzles or screens can reduce flow even if the filter cartridge is still functional.