How often should you change a water filter?
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Part of our tap water guide
The jug has sat on the worktop for months and nobody remembers when the cartridge went in. Does it matter? You can check how your own tap compares with a 20-in-1 test strip.
Short answer: Brita says to replace a MAXTRA PRO Pure Performance cartridge every 4 weeks or after 150 litres, and its LARQ bottle filter every 150 litres or about 2 months. The Drinking Water Inspectorate says a carbon cartridge not changed to the maker's schedule stops being effective and may leach chemicals or bacteria.
By Andrew Tomlinson, WaterKit · Last reviewed 29 October 2026
How often should you change a water filter?
As often as the manufacturer says, which for a Brita jug cartridge is about every 4 weeks. The Drinking Water Inspectorate (DWI) advises changing the cartridge in line with the manufacturer's instructions, so the intervals below are Brita's own, read on 29 October 2026. We have not checked other brands.
| Brita filter | Interval Brita gives |
|---|---|
| MAXTRA PRO Pure Performance (jug) | Every 4 weeks or after 150 litres |
| MAXTRA PRO in general (Brita FAQ) | At least every 4 weeks. 150 litres where hardness is 10 to 12 °dH, and sooner if the water is harder or use is higher |
| MicroDisc (carafes and bottles) | After four weeks |
| LARQ filter (bottle) | Every 150 litres or about 2 months |
These are the maker's own figures, not independent tests. Our guide on whether water filter jugs work covers what they can and cannot do.
What happens if you leave a cartridge too long?
The DWI says a carbon filter cartridge not changed in line with the maker's instructions will cease to be effective and may leach other chemicals or bacteria. It adds that ignoring the maker's advice on cleaning and changing causes a build-up of deposits, creates a breeding ground for bacteria and lets removed material leach back into the drinking water.
Brita describes it differently. It says a full filter simply stops filtering and does not leak impurities back. We cannot settle that difference, and changing on schedule fits both accounts.
How should you look after a filter jug?
Keep filtered water in the fridge and use it within a day. Writing about a jug of tap water kept in the fridge, the DWI says to throw away any unused water after 24 hours and clean the jug regularly. Brita says not to leave filtered water out of the fridge for more than a day, and to run water through a new MAXTRA PRO twice and discard the first two litres.
Why might your own tap differ from the area figure?
Because the area figure is an average. Your tap sits at the end of your own run of pipe, and the DWI's chlorine page gives several reasons.
- Chlorine. The DWI says companies typically keep it to 0.5 mg/l or less, and that homes near the treatment works may get a little more than homes several miles away. See why tap water can smell of chlorine.
- Hardness. The DWI says the taste of tap water can vary between regions because of differing hardness. Brita's 150 litres assumes 10 to 12 °dH and it says harder water shortens a cartridge's life. Check yours with our guide to how hard your water is.
- Standing water and fittings. The DWI advises drawing off a washing-up bowlful after several hours without use. It says a strong TCP-like taste may point to home plumbing.
“If you want to know how your own tap compares with the area figure, check it yourself, because an area figure is an average and your kitchen sits at the end of your own run of pipe. Chlorine, hardness and your home plumbing can all differ from house to house, so a quick look at your own water beats assuming it matches the leaflet.”
Can a test strip show whether your filter is still working?
Partly, for chlorine and hardness, and only if your tap water gives the pads something to show. Fill a clean glass from your cold kitchen tap and dip a strip. Do the same with water from the jug, then compare after 30 to 60 seconds, or enter the colours in the results portal. The table is WaterKit's own reading of the chart steps, not a method Brita gives.
| Pad | Chart steps (mg/l) | What a before and after can indicate |
|---|---|---|
| Free chlorine and total chlorine | 0, 0.5, 1, 3, 5, 10, 20 | With typical chlorine at 0.5 mg/l or less, your tap may already read 0 or the first step and the two strips may look alike. If the tap reads 0.5 or more and the jug reads 0, that fits a cartridge still taking out chlorine. |
| Hardness | 0, 25, 50, 100, 250, 425 | Brita says its cartridges reduce carbonate (temporary) hardness and calls Pure Performance moderate. If your tap reads 100 or more and the jug reads a step or more lower, that fits a cartridge still working on hardness. A soft tap gives nothing to compare. |
Some limits apply. We have not checked the hardness pad's unit basis, so compare only the two readings with each other. The strip cannot read lead at the UK limit, even though Brita says its cartridges reduce lead, so our lead pipes guide is the place to start there. We do not claim the strip for what a filter does to bacteria or fluoride, and the optional rapid coliform test is a presence screen on one sample, not a measure of a filter. The chart reads in set steps, so a change between two steps will not show, and no difference does not mean a cartridge has failed.
The area figure is an average, and the DWI says chlorine can be a little higher near the treatment works than several miles away, while Brita says harder water shortens a cartridge's life, so your own tap may differ. The chlorine and hardness pads are the ones that matter here. A tap reading 0.5 or more with a jug reading 0 fits a cartridge still taking out chlorine, while a jug that later reads the same as your tap would be a prompt to check the fitting date and the litres. Best pack: 20 strips, enough for ten before and after pairs across a few cartridge changes, £5.99 (or £10.99 with a bacteria test), with free 2nd Class delivery on every order. See the kit
Your water filter questions
How long does a water filter last?
It depends on the filter. Brita gives 4 weeks or 150 litres for MAXTRA PRO and 150 litres or about 2 months for LARQ.
How often should you change a Brita filter?
Brita's product page says every 4 weeks or after 150 litres, and its FAQ says at least every 4 weeks. The MicroDisc is also 4 weeks.
Is my water filter still working?
Check the fitting date and litres first. A before and after strip reading of chlorine and hardness may indicate a difference, as set out above. In the DWI pages we read we found no test for a spent filter.
How to tell when a water filter needs changing?
In the DWI pages we read we found no guidance on telling from the look or taste of the water, so go by the maker's date or litres. Brita says its MEMO, METER or Smart Light monitors the cartridge depending on the jug, and its pack QR code sets a 4-weekly calendar reminder.
Sources
- Drinking Water Inspectorate, Domestic water filters and softeners (change cartridges in line with the manufacturer's instructions, leaching, deposits, bacteria, black particles; undated page; read 29 October 2026).
- Drinking Water Inspectorate, Chlorine (typical residual 0.5 mg/l or less, variation with distance from the works, standing water, TCP-like tastes, fridge jug and 24 hours; undated page; read 29 October 2026).
- Brita UK, BRITA MAXTRA PRO PURE PERFORMANCE Filter Cartridges (4 weeks or 150 litres, fridge and 24 hours, clean regularly, lead reduction claim; undated page; read 29 October 2026).
- Brita UK, FAQ, Filters and Cartridges (10 to 12 °dH and 150 litres, at least every 4 weeks, spent filter, MicroDisc, LARQ, MEMO, METER and Smart Light, calendar reminder; undated page; read 29 October 2026).
- WaterKit, Water Test Kit (20-in-1 strip, 30 to 60 second read, rapid coliform test read after 24 to 48 hours, free 2nd Class delivery on every order) and results portal. The strip-chart table is WaterKit's own reading of the colour chart steps. Brita's figures are the manufacturer's own statements and not independent tests.
Contains public sector information licensed under the Open Government Licence v3.0.