A whole-house sediment filter does one job: it catches particles, sand, silt, rust flakes, scale grit, before they reach the plumbing, appliances, and any finer treatment downstream. It is the doorman of the water system, cheap and unglamorous, and most pressure complaints in filtered houses trace to a doorman nobody has relieved in a year. This reference covers the designs, the micron logic, placement, and the one maintenance signal that matters.
What sediment is, and is not
Sediment is suspended particulate: aquifer sand and silt on wells, rust and main-break debris on municipal lines, and the traveling grit that iron chemistry and pipe corrosion generate inside a house. What sediment is not is anything dissolved: hardness, sulfur odor, bacteria, nitrate, lead, and arsenic all sail through any sediment filter untouched, which is why the filter complements, and never replaces, the testing schedule and dedicated treatment. The filter protects equipment; chemistry and biology are other departments.
The three designs
Cartridge filters, the standard: a clear or opaque housing holding a replaceable element, spun polypropylene for depth-loading of mixed fine sediment, pleated for surface capture, higher flow, and, in washable versions, reuse. Simple, cheap, and consumable.
Spin-down separators, the pre-filter: a small clear cylinder with a screen (commonly 100 to 250 mesh) and a flush valve at the bottom, spinning heavier particles out of the stream and purging them with a few seconds of valve-opening instead of a cartridge change. The right first stage on sandy wells, protecting the cartridge behind it from doing coarse work.
Backwashing media filters, the heavy-duty answer: a softener-sized tank of filtration media that cleans itself on a scheduled backwash, no cartridges. Where sediment loads are chronic and heavy, or where an oxidizing media bed is already planned for iron duty, this class earns its plumbing.
Micron ratings without the mystery
A micron rating names the particle size the element targets: 100 microns is fine sand territory, 20 to 50 handles typical silt and rust duty, and 5 microns polishes toward visual clarity. Two honest footnotes: nominal ratings are approximate (absolute-rated elements exist and cost accordingly), and finer is not better, because every step down in microns is a step up in pressure drop and change frequency. The rational build on a dirty supply is staged coarse-to-fine, a spin-down or 50 micron stage ahead of a 5 to 20 micron cartridge, each stage doing the work it is shaped for.
Placement in the treatment train
The sediment stage goes first: after the pressure tank on a well (never between pump and pressure tank, where a loading filter would fight the pump), after the meter on municipal service, and ahead of everything it protects, softeners, carbon, UV lamps (whose effectiveness explicitly depends on clear water), and the household plumbing generally. Every housing deserves isolation valves and, ideally, a bypass loop, because a filter you cannot service without shutting the house down is a filter that gets serviced late. Pressure gauges on both sides of the housing convert maintenance from guesswork to arithmetic.
Downstream, the beneficiaries are every wet appliance in the house: fixture aerators and valve seats, the washing machine’s inlet screens, and the water heater, where imported grit joins the sediment economy that flushing exists to fight. Filtration upstream does not cancel the flush schedule; it just means the flush is fighting only the scale the water makes, not the sand it imported.
The maintenance signal
Filters report their condition as pressure drop. A loaded element steals flow, felt first at showers and top-floor fixtures, and the gauge pair makes it explicit: a spread widening 10 to 15 psi past the clean baseline is the change signal, whatever the calendar says. On wells, that commonly lands every 2 to 6 months; sudden loading after utility main work or a heavy-rain turbidity event is normal and temporary. A house with mysteriously fading pressure and a forgotten filter housing in the basement has, more often than not, just solved its own case, one branch of the general low pressure diagnostic.
The bottom line
Match the design to the load, stage coarse to fine, put it first in line with valves and gauges, and change elements on pressure drop rather than memory. A sediment filter is the cheapest employee in the water system, and like most doormen, it only gets noticed when nobody relieves the shift.