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Eco Purify Water

Replacing your filter cartridges.

A ten-step job you can do yourself in about twenty minutes. When it is due, how to finish without a drip, and the slip-ups behind most leaks and callouts.

BlogPublished 31 October 2026By the Eco Purify Water team

What you need to know first.

Turn off, release the pressure, swap, grease, refit, flush. That covers it.

You do not need a plumber for this. Nothing gets disconnected: each housing screws off its head much like the lid of a big jar. Plan on about forty minutes for your first cartridge change on a three-stage 20 inch system, and around twenty once you know the routine. Have these ready: the housing wrench supplied with the system, a set of three new cartridges, a bucket, a clean cloth and a small tube of food-grade silicone grease for the O-rings.

On the fitted Care Plan? Then you can skip this guide, because we send the set and our plumber puts it in. We wrote it for people on the delivered plan, for anyone who would rather do the job themselves, and for the curious who want to know exactly what the plumber does on the day.

Three 20 inch filter housings and replacement cartridges
In the direction of flow: sediment first, then carbon, then carbon block.

Knowing when they are due.

Watch the gauge for the sediment stage. Watch the calendar for the carbon stages.

  • The sediment stage is due at twelve months, or sooner if the pressure gauge reads roughly 70 to 100 kilopascals lower than it did on day one with the same tap running. Whichever comes first wins. If you live near mains works, expect it to fill up faster.
  • The carbon and carbon block stages go by the calendar: change them at twelve months. Carbon gets used up without moving the gauge, so the first clue is usually a chlorine smell creeping back into the shower.
  • Our recommendation is to swap all three at once. It is the easiest rule to live with: one date, one set, one job.

The ten steps.

This is the order our plumbers work in.

  1. 1

    Turn off the water to the filter

    Shut the inlet isolation valve first, then the outlet valve. If your system has a bypass valve, open it so the rest of the house still has water while you work. Write down the gauge reading before you begin.

  2. 2

    Let the pressure out

    Hold down the red pressure relief button on the head of the first housing until the water stops spurting and the gauge sits at zero. No relief button? Briefly open a cold tap inside the house instead.

  3. 3

    Take off the first housing

    Set the bucket under the sediment housing. Put the wrench around the sump and turn it to the left while you face the front of the system. Hold the sump as it drops free, because it has about four litres of water in it.

  4. 4

    Pull the old cartridge and wipe out the sump

    Lift the used cartridge out and put it in a bag. Empty the water, wipe the inside of the sump with your clean cloth and look for any grit sitting in the base. Keep detergent and bleach out of the sump.

  5. 5

    Inspect and grease the O-ring

    Ease the big O-ring out of the groove at the top of the sump and wipe both clean. Replace the ring if it looks flattened, nicked or has gone stiff. Give it a thin coat of food-grade silicone grease and press it back evenly into the groove. Petroleum jelly and plumber's grease are not suitable here.

  6. 6

    Put the new cartridge in

    Unwrap the new cartridge and stand it in the sump, centred over the standpipe or inside the moulded ring in the base. Make sure it sits level, so the top gasket meets the head once the sump is screwed back on.

  7. 7

    Screw the sump back on

    Raise the sump straight up to the head and turn it to the right by hand, still facing the front, until the O-ring seats, then give it one more quarter turn with the wrench. Go no further. Overtightening squashes the O-ring out of shape and creates exactly the leak it is there to stop.

  8. 8

    Do the same for the two carbon housings

    Repeat the process on the second (carbon) and third (carbon block) housings. Keep the order right in the direction of flow: sediment first, granular carbon second, carbon block last.

  9. 9

    Fill slowly and let the air out

    Shut the bypass. Crack the inlet isolation valve open a quarter turn so the housings fill gently, and press each relief button until you get water rather than air. Then open the inlet all the way, followed by the outlet.

  10. 10

    Flush, then look for leaks

    Run the bath or an outside tap for five to ten minutes. Expect grey water to start with: it is harmless carbon dust from the new cartridges and it clears. Dry off each housing and check the head seals for drips. Note the date and gauge reading on the care card in the cabinet.

Common slip-ups.

Six small errors behind almost every problem after a cartridge change.

  • Skipping the pressure relief button, then wrestling a sump that refuses to budge. Let the pressure out and it turns without a fight.
  • Cross-threading the sump on the way back. It should spin on by hand for the first few turns; if it does not, unscrew it and start over.
  • Fitting the carbon block in the first housing. It clogs within weeks. Sediment goes first, then carbon, then carbon block.
  • Leaving the outlet valve shut or the bypass open afterwards. You end up with no water, or water that skips the filter entirely.
  • Not flushing, then worrying about grey water. That is carbon fines, and they wash out in minutes.
  • Reusing a flattened O-ring. A new one costs a few dollars. A slow drip inside a cabinet costs far more.

Cleaning out a neglected system.

Only worth doing after months of sitting idle or if you see slime, and always with the cartridges out.

Only sanitise if the system has been sitting idle for months or you found slime in a sump. Do it before the new cartridges go in. With the housings empty, put about a tablespoon of unscented household bleach in each sump, screw them back on, fill, and wait ten minutes. Flush until you can no longer smell any chlorine, and only then fit the cartridges. Chlorine wrecks carbon media, so never sanitise with cartridges inside.

Common questions.

Plain answers, ready to use.

How often do whole house filter cartridges need replacing?

Replace all three together every twelve months. The only reason to change the sediment cartridge earlier is a gauge drop of 70 to 100 kilopascals, which tends to follow mains works in your street.

Is this a job for a plumber?

It does not have to be. The housings screw off their heads and nothing is disconnected, so anyone who is comfortable with a wrench can do it. If you would rather hand it over, the fitted Care Plan includes our plumber doing the change.

The water came out grey after I changed the cartridges. Is that normal?

Yes. Fresh carbon cartridges release fine carbon dust for the first few minutes. It is harmless and washes through. Run an outside tap for five to ten minutes before you use the kitchen tap.

Which way do I turn the housings to undo them?

Standing in front of the system, turn the sump to the left to remove it and to the right to refit it. If you have not released the pressure first, it will not move.

Which grease is right for the O-rings?

Only food-grade silicone grease. Anything petroleum-based makes the rubber swell, and that leads to leaks.

Can a sediment cartridge be washed and used again?

A pleated cartridge can be rinsed once or twice to buy some time if you are stuck, but its rating drops each time, and carbon stages cannot be rinsed at all. Given what a new cartridge costs, it is not worth doing.

Keep exploring.

Or hand the yearly change over to us.

Prefer we take care of it?

With the fitted Care Plan, the new set arrives before it is due and our plumber installs it, checks the seals and reads the gauge. One charge a year, and you can cancel anytime.

Request your fixed price0495 105 496