Filters
How often to change a water filter
Replace a filter by the manufacturer's rated capacity or time limit, whichever comes first, because a certification only applies within that life. EPA says an expired lead filter is less effective and WaterSense says unmaintained systems may make water quality worse.
The rule that applies to every filter
Certified filters are tested to a rated capacity and, in many cases, a time limit. After that point the certification no longer covers the filter. The agencies say the same thing in different words:
- EPA (lead): read the directions for when to replace the cartridge. “Using the cartridge after it has expired can make it less effective at removing lead.”
- EPA (PFAS): filters are only effective if maintained according to the manufacturer’s instructions for how long filters or membranes will last.
- Minnesota Department of Health: “All water treatment units require regular maintenance to work properly” and units that are not maintained lose effectiveness over time.
- EPA WaterSense: “unmaintained systems may make water quality worse.” Filters should be replaced according to the manufacturer’s instructions and recommended schedule.
Where to find your filter’s schedule
- The performance data sheet for the exact model lists the rated capacity in gallons or a time limit.
- The certifier’s listing (NSF, IAPMO R&T, WQA, CSA or UL) shows the claim and conditions (how to read it).
- The manual. Whichever limit arrives first, gallons or months, is the one that counts.
Examples from published listings
These come from the manufacturers’ own sheets and listings; check your own.
- Brita Elite pitcher filter: Brita’s listing says 120 gallons or about six months.
- Pentair FreshPoint F2000-B2B (under-sink carbon): the listing says to replace after 675 gallons or one year.
By type
| Type | What wears out | What to watch |
|---|---|---|
| Pitcher or faucet filter | The carbon and resin cartridge | Fixed gallon and month limits; replace even if it still flows |
| Under-sink carbon | Cartridges | Rated gallons; replace on whichever comes first |
| Reverse osmosis | Pre- and post-filters, and the membrane | Several parts with different lives; EPA says RO requires changing cartridges and the RO membrane |
| Whole-house carbon or sediment | Media or cartridges | Pressure drop and taste changes signal clogging |
Use a reminder
Write the replacement date on the cartridge when you install it and set a calendar reminder. If you use a test kit, WaterSense notes that periodic testing can help ensure a system is working (test options).
Sources
Not medical or legal advice. This guide summarizes public documents so you can ask better questions of your utility, your health department or a certified lab. For health concerns, talk to a clinician; for compliance questions, to your state drinking water program. Pages on this site that name products may earn a commission, as disclosed on the affiliate disclosure page.