Micron
µmmicrometermicrometre
A unit of length equal to one-millionth of a meter (10⁻⁶ m). Used to describe filter pore size — the threshold above which particles are mechanically captured.
Filter performance is described in microns because that's the scale at which mechanical filtration ends and chemical or membrane processes begin. A 5-micron sediment filter captures everything bigger than 5 µm; a 1-micron carbon block captures everything bigger than 1 µm and adsorbs many smaller chlorinated compounds.
What fits at each scale
- Hair, sand — 50–100 µm (visible to the eye)
- Pollen, fine silt — 10–40 µm
- Bacteria — 0.5–5 µm
- Viruses — 0.02–0.4 µm (below mechanical filtration; need RO or UV)
- Dissolved ions, PFAS — molecular scale (~0.0001 µm); only RO membranes reject these reliably
Choosing micron rating
A tighter filter isn't always better — it restricts flow and clogs faster. Standard configurations in our products:
- 5 µm sediment — first-stage protection for any system
- 10 µm carbon block (Q5421) — full-flow universal pre-filter
- 1 µm carbon block (Q5420) — fine post-filter for taste polishing
Above the membrane, microns are about flow vs protection trade-off. Below the membrane, they don't apply — RO operates by ion exclusion, not pore size.
Related terms
Reverse Osmosis A pressure-driven filtration process that pushes water through a semipermeable membrane, leaving dissolved minerals, salts, and most contaminants behind in a concentrate stream. Parts Per Million A ratio expressing concentration as one unit of solute per million units of solution. For dilute aqueous samples, 1 ppm ≈ 1 mg/L.