An overdue filter doesn't just stop working — it can actively make your water worse. Once saturated, carbon filters can release accumulated contaminants back into water (called desorption or breakthrough). Sediment filters that clog can rupture under pressure and dump trapped sediment downstream. Bacterial biofilm grows on any filter that sits unused, especially in warmer environments. The economics also work against waiting: a $30 filter changed on time protects $200+ of downstream RO membrane or other equipment from damage.
These are typical manufacturer recommendations. Check your specific product manual for exact intervals, and replace sooner if you notice degraded performance.
If your filter doesn't have a built-in indicator (or you don't trust it), use one of these tracking methods. Sharpie on the housing: write the install date directly on the filter housing or the cartridge itself. Simple, foolproof, doesn't depend on memory. Phone calendar with recurring events: set the reminder for one month before the change is due so you have time to order replacements. Subscription services: Brita, PUR, AquaTru, and several others offer auto-shipped replacement filters timed to typical replacement schedules. The convenience is worth the slight markup if you tend to forget.
Don't wait until it stops working completely.
| Filter Type | Replace Every | Notes |
|---|---|---|
| Pitcher (standard) | 2 months / 40 gallons | Brita, PUR standard filters |
| Pitcher (long-life) | 6 months / 120 gallons | Brita Longlast, Clearly Filtered |
| Faucet mount | 2-3 months / 100 gallons | |
| Under sink (carbon) | 6-12 months | Depends on usage and system |
| Refrigerator | 6 months / 200-300 gallons | |
| Whole house sediment | 3-6 months | More often with well water |
| Whole house carbon | 6-12 months | |
| RO pre-filters | 6-12 months | |
| RO membrane | 2-3 years | |
| Shower filter | 6-12 months | Or when flow decreases |