- →Three reliable indicators: (1) chlorine/chloramine taste returning to pre-filter levels, (2) noticeably reduced flow rate, (3) TDS no longer dropping 85%+ through an RO membrane.
- !An expired carbon filter doesn't just stop working — it can harbour bacteria, producing a musty or earthy taste. Replace immediately if a strange new taste appears that wasn't present when the filter was new.
- ✓For RO systems: a TDS meter ($15–30) gives you a definitive answer. Test before and after the membrane. Working = 85–96% TDS reduction. Below 70% = membrane degrading. Below 50% = replace membrane now.
- ✗If you've never noticed a difference from your filter: check whether it's the right type for your city's disinfectant. Standard pitcher filters in Sydney, Brisbane, or Adelaide (chloramine cities) provide limited taste benefit — this is a wrong-product problem, not a cartridge-age problem.
- →Calendar replacement is a backstop. For carbon filters: replace at manufacturer schedule OR when taste returns, whichever comes first. High-sediment water may exhaust cartridges faster than the calendar schedule.
Five signs your filter needs attention
Most water filters fail gradually rather than all at once — making it easy to miss that they’re no longer doing their job. Here are the clearest indicators something needs to change:
- Chlorine or chloramine taste returning: The most reliable indicator that your carbon media is exhausted. If your water starts tasting like the tap water did before the filter, the carbon adsorption capacity is full. Replace the cartridge.
- Noticeably reduced flow rate: Sediment build-up restricts flow through the filter media. In RO systems, a clogged pre-filter will significantly reduce output. A slow filter is often close to fully clogged.
- Strange new taste or smell that wasn’t there before: An expired carbon filter or cracked ceramic element can introduce bacterial growth — producing a musty or earthy taste. This is the filter making things worse, not better. Replace immediately and inspect the housing for mould.
- TDS reading no longer dropping (RO systems): A working RO membrane reduces TDS by 85–96%. If the gap between pre- and post-membrane readings has shrunk significantly, the membrane is degrading. Less than 70% reduction means service is needed.
- No change from when the filter was new — in a chloramine city: If you’ve never noticed a taste difference and you’re in Sydney, Brisbane, Adelaide, or GWW Melbourne, the filter may not be the right type for chloramine. Standard GAC pitcher filters have limited chloramine removal. This is a “wrong tool for the job” problem, not a cartridge age problem.
Interactive diagnostic — check your filter now
Answer five quick questions about your filter to get a specific assessment of whether it’s working, needs a replacement cartridge, or may have never been matched to your city’s water.
Replacement schedule by filter type
| Filter type | Cartridge replacement | Key indicator to replace early |
|---|---|---|
| Pitcher / jug filter | 2–3 months (or per manufacturer) | Chlorine taste returning; flow significantly slower |
| Tap-mount carbon filter | 3–6 months | Taste change; flow rate drop |
| Benchtop gravity filter (ceramic) | Ceramic: 1,000–3,000 L or when flow drops significantly | Flow rate drops; ceramic element visibly brown on outside |
| Under-sink carbon (2–3 stage) | Stage 1 sediment: 6 months; carbon block: 6–12 months | Taste change; pressure drop across filter |
| RO — sediment pre-filter | 6 months | Reduced RO output flow |
| RO — carbon pre-filter | 6–12 months | Taste change in product water |
| RO — membrane | 2–4 years | TDS reduction drops below 80% |
| RO — post carbon polisher | 12 months | Taste change in product water |
| Whole-home sediment (Big Blue) | 6–12 months | Visible pressure drop at taps |
| Whole-home carbon block | 12 months | Chlorine/chloramine taste returning at any tap |
| TAC media (scale prevention) | 3–5 years | Scale returning on shower heads and kettles |
| Shower filter | 6 months or ~10,000 L | Chlorine smell returning during showers |
| UV lamp | 12 months (regardless of use) | UV lamp life degrades with time even unused |
The wrong filter problem — when a filter never worked for your concern
A significant proportion of Australians who don’t notice a difference from their filter are in this category: the filter is working correctly but was never the right tool for their city’s primary water quality concern.
The most common version: a standard GAC pitcher filter in a chloramine city. The filter reduces free chlorine (not the main disinfectant), provides limited chloramine removal, and the water never tastes noticeably different — because the filter isn’t addressing what’s actually in the water. The filter isn’t broken; it’s the wrong product.
Check your city’s disinfectant using our water quality lookup tool, then verify your filter’s NSF certification at nsf.org against what it claims to remove.
For carbon filters: replace when taste returns or flow drops significantly, and at least annually regardless. For RO: test with a TDS meter annually — membrane performance below 80% TDS reduction means service is needed.
If you've never noticed a difference from your filter: check whether your filter type addresses your city's disinfectant type. A standard pitcher filter in Sydney (chloramine) provides minimal taste benefit. Use our suburb lookup to understand your water and our certifications guide to verify what your filter is actually certified to do.