Reverse osmosis replacement filters and membranes: what fits your system, when to change it, and what it costs a year in Australia

A reverse osmosis system is cheap to buy and dear to neglect: the membrane that does the work is protected by sediment and carbon pre-filters that have to be changed on time, and the membrane itself is a two-to-three-year part. What you buy depends entirely on whether your system uses standard housings or its own cartridges. Standard systems (Geekpure, iSpring and most generic tank units) take any 10 inch pre-filter and any 1812 membrane, so the Geekpure 5-stage set on Amazon Australia does the whole service in one box and the DuPont Filmtec BW60-1812-75 is the membrane with a stated rejection figure. Proprietary systems take their own: Philips’ AUT6103 cartridge is $399 at Bunnings for two years, Waterdrop’s X8 runs on a $44.99 F1G and a $69.99 F2, and Stefani’s membrane is $124 at Bunnings. We can’t show Amazon prices; the Amazon buttons show today’s.

Which replacement do you need: standard or proprietary?

Open the cupboard and count the housings. Three or four white 10 inch housings in a row plus a long thin tube on top is a standard 5-stage system: the housings take 2.5 x 10 inch sediment and carbon cartridges, the tube holds an 1812 membrane, and an inline post carbon hangs off the tank line. Any brand’s parts fit. One or two fat composite cartridges that twist out of a slim box is a proprietary system (Philips, Waterdrop, Puretec), and only the maker’s cartridge fits.

For a standard system, the Geekpure RO5-5 set is the simplest service: a PP sediment, a granular carbon, a carbon block, a 75 GPD membrane the listing calls NSF certified, an inline post carbon, two fittings and tape, all individually sealed, with feed limits printed (40 to 100 psi, 5 to 45°C, pH 3 to 11, TDS to 2,000 ppm), which matter on a bore. The post carbon is a 1/4 inch NPT inline, so check yours. The iSpring F4 is the membrane-less equivalent for stages one, two, three and five, but its Amazon page showed no featured offer when we checked, and the iSpring F9K is a year of pre-filters plus alkaline filters for the six-stage RCC7AK, no membrane, five left in stock.

For the membrane alone, buy the Filmtec BW60-1812-75: DuPont’s standard 1812 element, 75 GPD at 50 psi and 90 at 60, 99% stabilised salt rejection, with a QR code that the DuPont app verifies, dispatched in five to six days. The iSpring MC7 is the same size and type, in stock, with no rejection figure on its listing.

When to change what

Pre-filters first and on schedule, because a blocked carbon block starves the membrane of pressure and a spent one lets chlorine through to a membrane that chlorine destroys. Six to 12 months is the usual interval; Philips lists three to six months per stage for its AUT515 set, Waterdrop 12 months for the F1G and six for the F2. The membrane goes two to three years on town water if the pre-filters were kept up, less on a bore or tank. The post carbon, which polishes taste after the tank, yearly.

The honest test is a TDS meter, which our test-kit guide covers for under $30: a healthy membrane cuts dissolved solids by 90% or more, and when the filtered reading climbs toward the tap reading, or the tank takes much longer to fill, the membrane is done. Change the pre-filters first and retest before you buy a membrane, because the symptoms are the same.

What a year costs, system by system

From the prices we loaded on 1 November 2026. A Waterdrop X8 on its own filters: about $185 a year (one F1G at $44.99, two F2 at $69.99). A Waterdrop A2: $99 a year for the A2RF-RO, membrane included; the C1S’s C1RF is $119.99 and was sold out at Waterdrop Australia. A Philips AUT6103: about $200 a year, being half of the $399 two-year cartridge. A Stefani undercounter 5-stage: its $124 membrane every few years plus the 250 mm pre-filters from our Stefani cartridge guide, about $62 a year at Bunnings. A standard Geekpure or generic system: one Amazon set a year with a membrane every second or third set; we can’t print the Amazon figure, but it’s the cheapest service on this page by a margin, which is the real case for a standard system that the reverse osmosis guide balances against its lack of WaterMark.

The one trap

Changing the membrane and leaving the old pre-filters in. A $60 membrane behind a chlorine-saturated carbon block lasts months, not years, because the membrane’s polyamide surface is damaged by free chlorine the carbon was there to remove. Service the pre-filters with the membrane, flush the new set for the 30 minutes Geekpure’s listing asks for, then test the TDS a week later and write the numbers on the housing.

What we left out and why

• iSpring F4 four-filter kit (Amazon Australia). The right kit for a standard 5-stage without a membrane, but no featured offer on 1 November 2026.
• Geekpure 50 GPD and 100 GPD sets (Amazon Australia). Same set with a slower or faster membrane; match the GPD on your old membrane’s label.
• Generic ULP1812-75 membranes (Amazon Australia). A dozen unbranded listings; the Filmtec and iSpring are the two with a maker behind them.
• APEC, Culligan, GE and Bluevua sets (Amazon Australia). For systems not sold in Australia.
• Philips AUT515, AUT514, AUT521 and AUT619 sets. Philips’ Australian site lists the AUT515 for the AUT9510 with no price, and Bunnings didn’t stock any of them on the day.
• Waterdrop C1RF. $119.99 at Waterdrop Australia, sold out when we checked, and the page’s lifespan fields still held template text.
• Remineralising and alkaline inline cartridges. In the alkaline water filter guide.