Quick take
Pressure drop must be evaluated at the household flow rate you actually use. A system that looks fine at 5 GPM can become restrictive at 10–15 GPM.
Pressure drop rises with flow
As more water is pushed through media or a cartridge, resistance increases. This is why manufacturer service-flow data matters more than a zero-flow pressure number.
Loaded prefilters are common restrictions
Sediment cartridges can clog long before the main media is exhausted, creating a noticeable decline in shower and fixture flow.
Pipe size and fittings matter
A 1-inch treatment system installed into restrictive 3/4-inch piping, small valves or tight elbows can still have poor whole-house flow.
Do not solve a clog with a booster pump
A booster pump can address inadequate source pressure, but it should not be used to hide an undersized or dirty filter. Diagnose the restriction first.