If you've been shopping for water filters, you've probably noticed micron ratings on the packaging — 0.5 micron, 1 micron, 5 micron. But what do these numbers actually mean, and which one do you need? Here's a straightforward explanation.
A micron (micrometre) is one-millionth of a metre. To put it in perspective, a human hair is about 70 microns in diameter. Water filter micron ratings describe the size of the smallest particle the filter can reliably capture — the lower the number, the finer the filtration.
Common Micron Ratings and What They Remove
Micron Rating
What It Removes
Typical Use
50+ microns
Large sediment, sand, rust
Pre-filter / coarse sediment
5 microns
Fine sediment, silt, dirt
Whole house pre-filter
1 micron
Fine particles, some bacteria
Under sink, benchtop
0.5 microns
Most bacteria, Giardia, Cryptosporidium
Ceramic dome filters, benchtop
0.2 microns
Most bacteria and some viruses
High-purity applications
How Many Microns Do You Need?
Town water (Sydney, Melbourne, Brisbane, Adelaide, Perth): A 0.5–1 micron filter is appropriate for most households. Town water is pre-treated, so the main concerns are chlorine, taste, and fine sediment — not bacteria.
Tank or rainwater: Go to 0.5 microns or lower. Tank water can contain bacteria, Giardia, and Cryptosporidium, especially after heavy rain. A ceramic dome filter at 0.5 microns is a popular choice.
Bore water: High sediment loads mean you’ll want a coarse pre-filter (5–10 microns) followed by a finer main filter. A whole house filter system with multiple stages is the most practical solution.
Absolute vs Nominal Micron Ratings
One thing worth knowing: micron ratings can be nominal (removes ~85% of particles at that size) or absolute (removes ~99.9% of particles at that size). For drinking water, look for absolute-rated filters where possible — particularly for bacteria removal.
