Read the old cartridge first
It is the best diagnostic available and it costs nothing. Cut it open or at least look closely before it goes in the bin.
Loaded evenly with fine brown or tan silt — ordinary sediment. If it is loading faster than it used to, something upstream has changed.
Coarse grit or sand — on a well, that usually means the pump is drawing from lower in the water column or the well is producing more solids. On city water, it often follows main work or a repair nearby.
Orange or rust-coloured staining — iron. This is a chemistry problem rather than a particle one, and a sediment filter is the wrong tool for it.
A slimy or gelatinous coating — iron bacteria or biofilm. Filtration alone will not resolve it.
Loaded heavily on one end only — channelling, meaning water is finding a path rather than distributing through the media. Usually a seating or sizing issue.
Clean but flow was still poor — the filter was never the restriction. Look at valves and pressure instead.
Worth knowing
A cartridge that is clean when you remove it is important information. It means the pressure complaint has another cause — a partly closed valve, a failing pressure regulator, or something else entirely — and replacing the filter is treating the wrong thing.
Micron rating: finer is not better
This is the most common mistake, and it is an understandable one. A 1-micron cartridge sounds superior to a 20-micron. As a first stage, it is usually the wrong choice.
A fine cartridge captures more, which means it fills faster. Put a 1-micron filter on water carrying ordinary sediment and it will clog in weeks — not because it is defective, but because it is doing exactly what it was asked to.
The right approach is staged. A coarse cartridge first — 20 to 50 micron — takes the bulk of the load and is cheap to replace. A finer cartridge after it handles what is left and lasts far longer because most of the work has already been done.
One 5-micron cartridge doing everything is the arrangement that clogs monthly. Two stages usually cost less per year and give better flow throughout.
Housing size and flow
A standard 10-inch housing is what most systems get by default, and on a whole house it is frequently too small.
Two things go wrong. Capacity: a small cartridge holds less material, so it fills sooner regardless of water quality. And flow: every filter creates resistance, and a small housing at high flow produces a noticeable pressure drop even when the cartridge is relatively clean.
The symptom that identifies this is pressure that is fine early in the morning and poor when several fixtures run — the same intermittent pattern that points at undersizing rather than fouling.
A larger housing — the big blue 20-inch type — holds substantially more and flows better. Two in parallel do better still. Either beats replacing a small cartridge every six weeks.
When it is not a filter problem
Several things imitate a clogged filter, and it is worth ruling them out before buying anything.
A partly closed valve either side of the housing, commonly left that way after the last cartridge change.
A failing pressure regulator, which drops pressure across the whole house. The test: compare pressure at a hose bib upstream of the filter against one downstream. If both are low, the filter is not the restriction.
A bypass valve partly open, which reduces effective filtration while appearing to help pressure.
A pressure drop that was always there and has only just been noticed, often after a filter was installed — that one is the system working as designed rather than failing.
The gauge reading either side of the housing is the definitive test and takes two minutes.
Iron, and the case a filter cannot win
Worth separating because it is common on Hill Country wells and because a sediment filter is genuinely the wrong equipment for it.
Dissolved iron is invisible in water and precipitates when it meets air or an oxidiser. So it enters the filter dissolved and becomes particles inside or after it — which is why a cartridge can stain orange while doing nothing useful.
Iron above roughly 0.3 ppm needs oxidation and dedicated filtration, or a specialty resin. Handling it with sediment cartridges means changing them constantly and still having iron in the water.
It also matters downstream: iron fouls softener resin, and once that has happened the resin generally does not recover. On a well, sequencing is sediment, then iron, then softening — covered in well water plumbing.
If the cartridge keeps coming out orange, the answer is a water test rather than another cartridge.
What to do about it
Test the water if you have not. Hardness, iron, pH and total dissolved solids. It costs little and it determines what equipment is appropriate — everything else is guessing.
Then stage the filtration properly: coarse first, fine second, in housings sized for the house rather than for the shelf they came off.
Date every cartridge when you fit it. “It seems like it clogs fast” is an impression; “six weeks in summer, four months in winter” is data, and the seasonal difference itself often points at irrigation drawing more water through the system than anyone accounted for.