Quick take
A common interval is every 6–12 months for sediment and carbon stages, but the exact system schedule and feed-water quality should control the decision.
Sediment filters
Sediment stages often last around 6–12 months. Heavy rust, silt or construction debris can shorten that interval and cause noticeable pressure drop.
Carbon prefilters
Carbon protects many RO membranes from chlorine and improves taste/odor. Exhausted carbon can expose a chlorine-sensitive membrane to damage.
Signs replacement is due
Lower production rate, pressure drop, odor breakthrough or a manufacturer timer are common signals.
Why brand schedules differ
Modern tankless systems often combine stages into proprietary cartridges, so replacement timing can be model-specific.