The two signs that mean it is due
The flow has slowed. A cartridge works by catching things. Everything it catches stays in it, so over time less water gets through for the same pressure. A filtered tap that used to fill a glass briskly and now takes its time is telling you exactly what is going on.
The taste is back. Carbon is what takes the chlorine taste out, and carbon has a finite capacity. When it is used up the water keeps flowing but stops being treated — and because it happens gradually, most people notice it as "the water has gone off again" rather than as a filter reaching the end of its life.
Either sign on its own is enough to ring about. You do not need to check anything, take anything apart, or work out which stage it is. That is the job.
How often it is actually due
Manufacturers generally nominate a period, and around twelve months is the common one. Treat that as the starting point rather than the law.
What moves it is how much water goes through the cartridge. A household of five that drinks and cooks from a filtered tap all day gets through a cartridge faster than a couple who use it for tea. And if the filter was plumbed back through the main kitchen mixer rather than to a dedicated tap, every rinsed plate and every filled saucepan has been running through it too — those cartridges come up for replacement sooner, and that is normal rather than a fault.
Sediment matters as well. A cartridge that is catching a lot of particles blocks up on flow before the carbon is used up on taste. Which of those you have got is something the plumber can tell on site.
On a reverse osmosis system there is more than one item and they do not all run out together — the pre-filter stages protecting the membrane are changed more often than the membrane itself. More on reverse osmosis
Why a licensed plumber does the whole-house ones
An under-sink cartridge change is a small job in a cupboard. A whole-house one is not the same animal.
The housings on a whole-house system sit on the incoming water main, usually outdoors, at mains pressure. Changing a cartridge means isolating the unit, taking the pressure off it safely, getting a bowl off that has been under load and in the weather since the last service, replacing seals that have been compressed for a year, and putting it all back so it holds. If the system has a bypass built in, the house keeps water while that happens. If it does not, it does not.
Bowls that have not been off for a couple of years can be genuinely stubborn, and the tools and the technique for that are the reason this is a trade job rather than a Saturday one. When it goes wrong it goes wrong on the line feeding the entire house.
Plumbing Licence 8396, held by Tim, who does the work himself. Whole house water filter installation
What it costs
Less than a new system, which is the main thing worth saying.
Beyond that it depends on which system you have, how many stages it runs, which of them are actually due, and whether the housings come apart cooperatively. A single under-sink cartridge is the cheap end. A multi-stage whole-house unit that has not been serviced in several years is a longer visit.
We are not going to put a figure on a web page for a system we have not seen. A licensed plumber comes out at no charge, looks at what you have, and leaves you with a written price before anything is touched. Transparent pricing, no hidden costs.
If you do not know what you have got
That is completely normal, particularly in Kardinya. This is a suburb of established detached houses — 2,978 of its 3,772 private dwellings were separate houses at the 2021 Census — built out in quadrants between October 1967 and the late 1980s. Plenty of those kitchens have been renovated at least once since, and a filter that came with a renovation or with the previous owners is often a complete unknown to whoever lives there now.
You do not have to identify it. Ring, and the plumber works out what is under there when he arrives. If it turns out to be a system worth keeping, he changes the cartridge. If it turns out to be something long past its useful life, he tells you that instead and you decide.
While he is there
Two things usually worth sorting at the same visit, because they cost less done together than done twice.
Isolation. A filter you cannot shut off on its own is a filter that turns every future service into a whole-house event. If the isolation is missing or seized, that is the moment to fix it.
Access. Housings mounted somewhere you cannot get a bowl off are a design problem, not a servicing problem. If yours is one of those, the plumber will say so and tell you what it takes to move it.
Never serviced it at all?
Then it has probably been doing very little for a while. That is worth knowing rather than worth feeling bad about — it is the most common thing we come across on filters that came with a house.
The fix is the same either way. See the systems we install · Common questions