How often should I change my coffee machine water filter?
Two months for most machines. Three for Sage and Breville. But that is only half the instruction, and the half people miss is the one that matters.
Why is the interval a limit rather than a target?
Every manufacturer states it the same way: a time or a volume, whichever comes first.
- De’Longhi: every 2 months, or about 50 litres
- Sage and Breville: every 3 months, or about 40 litres
If you pull four cups a day, you will hit the volume before the time. If you have been away for three weeks, you will hit the time with the volume barely touched. Whichever arrives first is the one that counts.
That “whichever comes first” is why the number on the box is a ceiling rather than a plan. Nobody is telling you a filter is good for exactly two months. They are telling you not to go past it.
What actually wears out inside the filter?
A coffee machine filter is doing two unrelated jobs, and each one runs down on its own clock.
Ion-exchange resin is what softens the water. It swaps the calcium and magnesium that cause limescale for something harmless, and it fills up as it goes. Hard water fills it faster. In a very hard area you can genuinely exhaust the resin before the two months are up.
Activated carbon is what fixes the taste. It adsorbs chlorine and the organic compounds that make tap water taste of tap water. It does nothing about hardness at all, and hardness does nothing to it.
The two get conflated constantly, including by people selling filters. They are separate materials doing separate work.
Does soft water mean I can leave it in longer?
Here is the part that catches people out. If hard water exhausts a filter faster, it seems to follow that soft water should let you stretch the interval. It does not.
The time limit is not about hardness. It is about a wet cartridge sitting in a warm tank. Carbon runs down on volume and exposure regardless of how soft your water is, and a spent filter in standing water is not a neutral object — it is somewhere for things to grow. That clock ticks at the same speed in Aberdeen as it does in Ipswich.
So hardness can move the interval in one direction only. Very hard water is a reason to change it sooner. Soft water is not a reason to change it later.
We build this into our own guidance: where our hardness adjustment would push a recommendation past the manufacturer’s limit, we clamp it back. You will never see us suggest 90 days for a filter its maker rates at 60.
What does soft water actually change?
If your water is genuinely soft, the honest position is that a filter is doing less for you. There is not much limescale to prevent. What you are buying is the taste improvement from the carbon — which is real, and is the reason plenty of people in soft-water areas still use one.
What you should not be told is that you are protecting the machine from limescale that was never going to form. In a soft-water area that is a sales pitch, not a fact.
How do I find out how hard my water is?
UK water hardness varies enormously over short distances — parts of London and the South East run very hard, much of Scotland, Wales and the South West runs soft. Your water company publishes the figure for your postcode, usually under “water quality”.
It is worth two minutes. It is the difference between changing a filter every six weeks and every two months, which over a machine’s life is a meaningful number of cartridges.
What is the short version?
- Change it at the manufacturer’s interval, or the stated volume, whichever arrives first
- Very hard water: change it sooner
- Soft water: change it at the same interval, not later
- The interval is a ceiling, and there is no prize for reaching it exactly
If you want the specific interval for your machine rather than the general rule, the filter finder has it per model, along with the part number and whether a compatible filter will work at all.