A filter retains contaminants. It does not destroy them: it accumulates them. Past a certain point it stops protecting, increases the pressure drop, and can release what it had captured.
The usual intervals
- Sediment cartridge: 3 to 6 months depending on the turbidity of the water.
- Activated carbon: 6 to 12 months.
- Reverse osmosis membrane: 2 to 3 years if the pre-treatment is correct.
- UV lamp: around 12 months, even if it is still lit.
- Softener resin: several years, with regular regeneration.
These are orders of magnitude
Actual life depends on the volume treated and the quality of the incoming water. Heavily loaded water shortens these intervals; light use can extend them — though never beyond the health limit, since a damp, little-used filter is a favourable environment for bacterial growth.
The signals not to ignore
A drop in flow, the return of a taste or an odour, cloudy water, a rise in differential pressure: each of these signs indicates a filter at the end of its life, whatever the schedule says.
The special case of the UV lamp
A UV lamp goes on emitting visible light long after it has lost its germicidal effectiveness. It is replaced on schedule, not when it goes out.