Buyer guide · Updated 22 Oct 2026 · By the Filtsap technical team
When to replace a filter cartridge: 5 signs and the pressure-drop rule
Short answerReplace a filter cartridge when the pressure drop across the housing rises 1–1.5 kg/cm² (15–20 psi) above its clean value, when flow falls noticeably, or when it reaches the change-out interval your plant has set. As a guide, RO pre-filters last 15–45 days, domestic sediment filters 3–6 months and carbon cartridges 3–6 months.
The 5 signs
- Pressure drop: the inlet-to-outlet gauge difference has risen 1–1.5 kg/cm² over clean.
- Lower flow: the RO or process line takes longer to fill or the pump struggles.
- Colour: a white cartridge turns brown or black all the way through, not just on the surface.
- Taste or odour returns: the carbon cartridge is exhausted.
- Downstream problems: the RO membrane fouls faster or the SDI rises.
Typical change-out intervals
| Use | Typical life |
|---|---|
| Industrial RO pre-filter (5 µm) | 15–45 days |
| Commercial jumbo cartridge | 1–3 months |
| Domestic sediment (10") | 3–6 months |
| Carbon cartridge | 3–6 months |
| Pleated polishing cartridge | 1–6 months, at 15–35 psi ΔP |
Don't wash and reuse PP cartridges
Washing a spun cartridge pushes trapped dirt deeper, or tears the fibres so that dirt passes straight through. It costs less to replace it than to damage an RO membrane.
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FAQs
Why does my cartridge clog in a few days?
Usually the micron is too fine for the water, or there is no coarser stage before it. Add a 20–25 µm wound or bag pre-filter in front of it.