How often should under-sink and reverse-osmosis filters be replaced?

Each stage can have a different schedule

An under-sink system may use one cartridge, while a reverse-osmosis system can use sediment, carbon, membrane, and post-filter stages. Do not replace every part on one generic six-month schedule unless the system manual specifically says to do so.

The correct interval depends on the exact system, rated capacity, water quality, and household use. Record the installation date for each stage separately.

Use the manufacturer schedule as the baseline

Prefilters often need attention before the RO membrane because they protect it from sediment and chlorine. A membrane may last longer, while a polishing post-filter may follow its own interval. Sealed quick-change systems can use a different schedule from standard housings.

• Check the system manual and cartridge label
• Track gallons when the system includes a usage monitor
• Replace sooner if the manufacturer identifies reduced flow as a warning
• Never extend a schedule solely because water still looks clear

Watch for changes and inspect for leaks

Reduced flow, unfamiliar taste or odor, an indicator alert, or a known change in source-water quality can justify an earlier check. These symptoms can also indicate pressure, plumbing, tank, or membrane problems, so replacing a random cartridge may not solve them.

After any replacement, follow the flushing and sanitizing instructions for the exact system and inspect every housing and fitting for leaks.