Slow filtered-water flow can come from a loaded filter, incorrect installation, low inlet pressure, trapped air, or a kinked line. Before buying another cartridge, compare flow before and after the filter when possible and inspect the accessible installation.
Check whether the slowdown started after a filter change
A filter installed backward, left with a shipping cap, or not fully seated can restrict flow from the first use. Check the part number, direction, and fit against the manual and do not force connections.
An older filter may be loaded with sediment
If flow declined gradually and the cartridge is near its rated capacity or interval, restriction may be in the filter media. Replace it according to the manufacturer and see whether flow recovers after flushing.
Check inlet pressure, valves, and kinked tubing
A partly closed valve or kinked tube limits flow even with a new filter. Compare other fixtures or upstream supply where possible to determine whether the filter system is truly the restriction.
Persistent low flow with a new filter calls for system diagnosis
If installation, pressure, and the cartridge are correct, an internal valve, reverse-osmosis tank, or another component may be limiting flow depending on the system. Do not alter regulators or pressurized housings without instructions; use qualified service when appropriate.