The complete guide
Filter indicators, and when to actually change a cartridge
Almost every filter sold today has some kind of change reminder. Very few people know what their reminder is actually measuring, which is why so many households are drinking through a cartridge that stopped working weeks ago.
The three kinds of indicator
Time-based. A small clock that starts when you fit the cartridge and signals after a set period — four weeks, typically. The BRITA Memo on this tank is one of these. It is simple, it never fails mechanically, and it is completely indifferent to how much water you have used.
Volume-based. Counts litres or fills as they pass. More accurate in principle, but the counting mechanism has to be reset correctly and can drift.
Flow or pressure sensing. Found on plumbed-in systems, where the filter's condition can be inferred from how it behaves under pressure. Most accurate, most expensive, not something you find on a gravity tank.
Why time-based is usually fine, and when it is not
For a household using roughly the average amount, a four-week timer and a 150-litre cartridge line up neatly. The design assumes you get through about 5 litres a day, and most families do.
It goes wrong at the extremes:
- Heavy use. A household of five running this tank hard could hit 150 litres in under three weeks. The indicator will still say you have a week left, and it will be wrong.
- Light use or a holiday. Two weeks away means the clock keeps running while no water passes through. The indicator will demand a change you do not need — although if the cartridge has sat wet and warm for a fortnight, changing it anyway is not a bad instinct.
The fix is to use the indicator as a prompt to think, not an instruction.
The signs that override any indicator
Regardless of what the display says, change the cartridge if:
- Flow slows noticeably. Loading media is the commonest cause.
- Chlorine taste returns. The carbon is saturated. This is the clearest signal there is.
- Water looks cloudy or has visible particles.
- There is any smell from the filtered chamber.
Habits that make a cartridge last its rated life
- Prime it. Soak a new MAXTRA PRO as instructed and discard the first couple of fills. It clears loose carbon fines.
- Keep the lower chamber clean. This is the part people neglect. Filtered water sitting in a warm tank grows a film regardless of how good the cartridge is. Everything but the digital indicator goes in the dishwasher — use that.
- Do not let it stand for a week. If you go away, empty it, and give the cartridge a rinse and a fresh prime when you come back.
- Fill from the cold tap only. Warm water damages the media.
Where the reminder matters most
On a jug you notice problems quickly, because you handle it constantly. On an 8-litre tank with a tap you interact with it far less — you fill it and forget it, which is the entire appeal and also exactly why the cartridge slips your mind. On a dispenser this size, an indicator is not a gimmick; it is the thing standing between you and a filter that has been decorative since last month.
If you would rather have the reminder built into a slimmer unit, the Waterdrop WFD-04L carries a smart indicator in a narrower body.