- →Sediment filters work by physical size exclusion — particles larger than the pore size are blocked. No chemistry. No taste improvement. Pure particle removal.
- →Pore size is rated in microns. 5 micron is standard for whole-home. 0.5 micron for Crypto/Giardia. 0.2 micron ceramic for bacteria removal.
- ✗Sediment filters do not remove chlorine, chloramine, fluoride, hardness, bacteria (except at 0.2 micron), taste or odour. They remove particles only.
- →Always the first stage — it protects the more expensive carbon and RO stages downstream from fouling.
- !Replace when flow rate drops — that is more reliable than a calendar. Bore water may exhaust a cartridge in 1–4 months.
What a sediment filter actually does
A sediment filter is the simplest type of water filter. It works by physically blocking particles that are too large to pass through its pores — the same basic idea as a coffee filter or a sieve, but much finer. Water is pushed through a polypropylene or ceramic element with millions of tiny pores at a defined size. Particles larger than that pore size get blocked; water and dissolved chemicals pass straight through.
What micron ratings mean
Sediment filters are rated in microns — thousandths of a millimetre. The lower the number, the finer the filter and the faster it clogs.
- 50 micron — coarse. Large particles, sand, debris. Common first stage for bore water with heavy load.
- 20 micron — coarse sediment, rust flakes, larger silt.
- 5 micron — the most common rating. Fine sediment and rust. Protects the carbon stage downstream.
- 1 micron — very fine particles. Used before RO membranes.
- 0.5 micron — removes Cryptosporidium and Giardia by physical exclusion.
- 0.2 micron ceramic — removes bacteria as well as protozoa.
For reference: a human hair is approximately 70 microns. Giardia is 8–15 microns. Bacteria are 0.5–5 microns. A 5-micron filter does not remove bacteria — it removes visible particles only.
Where it sits in a multi-stage system
Sediment filters are almost always the first stage in any multi-stage system. The reason is protecting the more expensive stages downstream. A carbon block that receives turbid water will clog in weeks instead of lasting 12 months. An RO membrane exposed to particles fouls rapidly. A UV lamp cannot penetrate turbid water effectively.
In a whole-home system, the sediment stage installs first — before carbon, TAC, and UV. In an under-sink RO system, the sediment cartridge protects the membrane and is replaced every six months.
When to replace a sediment filter
The most reliable indicator is reduced flow rate or water pressure — not the calendar. As the element traps particles it progressively restricts flow. In whole-home systems you will notice weaker pressure at taps; in under-sink systems slower fill times.
Typical intervals: metro town water 6–12 months; rainwater tank 3–6 months; bore water 1–4 months depending on iron and sediment load. Replace when flow drops, regardless of time elapsed.
Most sediment cartridges cannot be effectively cleaned and reused. Rinsing only cleans the surface — particles trapped deep in the media remain. Replace rather than rinse, especially for bore or tank water.
For metro town water a 5-micron cartridge is sufficient. For bore water or rainwater tank, use a coarser pre-filter first, then 5 micron. For Crypto/Giardia protection without UV, you need 0.5 micron. For bacteria removal, 0.2 micron ceramic only.
Sediment filters do not improve taste, remove chlorine, reduce hardness, or address any chemical concern. They are a prerequisite for the stages that do.