Do I need a whole-home system or just an under-sink filter?

Under-sink covers the kitchen drinking tap. A whole-home system covers every tap, the shower, the washing machine, and outside hose bibs. If chlorine is irritating skin or hair, if your hot-water system is collecting sediment, or if you want filtered water on every outlet, the whole-home option is the right call. If you only want clean drinking water, an under-sink filter is cheaper to buy and to run.

Where does the system get installed?

On the cold-water mains, after the meter and before the line splits to internal taps. Most installs sit on an external wall or in the garage so cartridge changes do not require entering the house. Whole-house systems must be plumbed by a licensed plumber for the install to comply with state regulations and warranty terms.

What size system do I need for a typical Australian home?

Match the housing size to peak flow. A four-bedroom home with two bathrooms typically needs 20 inch x 4.5 inch (Big Blue) housings to keep flow up when multiple outlets are running. Smaller properties or low-flow holiday homes can run 10 inch x 2.5 inch. Every product page lists rated flow rate in L/min.

How often do whole-home cartridges need replacing?

Six to twelve months for sediment and carbon stages on town water. Three to six months on rainwater or sediment-heavy supplies. Pressure drop is the giveaway — when you notice flow slowing at fully-open taps, the sediment cartridge is loaded. Most whole-home housings have a pressure release button to make changes a five-minute job.

Whole Home Water Filtration Systems

A whole-home water filtration system sits on the cold-water mains and treats every drop of water entering the house. The kitchen drinking tap, the shower, the washing machine, the outside hose — every outlet runs filtered. It is the only way to remove chlorine before your skin and hair get to it, and the only way to protect downstream appliances from sediment.

Whole-home systems pair well with under-sink reverse osmosis if you want the strictest treatment on the drinking tap (RO downstream of whole-home pre-filtration is the cleanest water you can produce at home).

The standard configurations:

Two-stage — sediment + carbon. Removes the bulk of chlorine, taste, and grit. Suits most town-water installs.
Three-stage — sediment + carbon + KDF/scale-control. Adds longer cartridge life and starts on hard-water issues.
Three-stage with UV — sediment + carbon + UV. The standard rural and bore-water setup. UV destroys bacteria and viruses without chemical addition.

What to look for

Three specs decide whether a whole-house system actually does its job, or just looks the part on the wall.

Housing size — Big Blue or standard?

Big Blue is the industry name for 4.5"-diameter cartridge housings. Standard housings are 2.5" diameter. Big Blue housings hold roughly five times more cartridge media, which means more contact time with the water, more capacity before the cartridge is loaded, and less pressure drop at peak flow. For any home with two or more bathrooms, or anywhere multiple outlets run at once, Big Blue is the right baseline. Standard 2.5" housings are fine for low-flow holiday homes, granny flats, or single-occupant cottages.

The two common Big Blue lengths are 10" and 20". A 20" housing roughly doubles cartridge life over a 10" of the same configuration.

Micron rating

The micron rating on a sediment cartridge is the smallest particle it captures. Lower number = finer filtration, but also faster pressure drop as the cartridge loads.

20 micron — coarse pre-filter for very dirty water (rural tank, post-flush sediment events). Long life, low pressure drop.
5 micron — the standard whole-house sediment rating. Catches most visible grit and rust without choking the flow.
1 micron — fine polishing stage, usually paired with a 5 micron pre-filter. Worth it for noticeably sediment-heavy supplies.

For most town-water installs, a single 5 micron sediment stage is enough. Tank or bore water benefits from a 20 micron pre-filter ahead of a 5 micron stage to extend cartridge life.

Carbon type — GAC, block, or catalytic

Not all carbon is the same. Three types matter:

Granular activated carbon (GAC) — loose granules in a cartridge. Cheapest, fastest flow, shortest life. Good for chlorine taste on town water. Not effective against chloramine.
Carbon block — the granules are compressed into a solid block. Slower flow but much higher contact time, finer filtration (often acts as a 5 micron sediment stage too), and removes more contaminants per litre. The standard pick for most whole-house second stages.
Catalytic carbon — specifically processed activated carbon designed to break down chloramine. Required if your water authority uses chloramine (Sydney, Melbourne, Brisbane, Adelaide, Canberra). Standard GAC and standard carbon block do not remove chloramine reliably at whole-house flow rates. See chloramine and PFAS for the full picture.

Flow-rate sizing rule

Match the system to peak demand, not average use. The rule of thumb for Australian homes:

One- or two-bedroom unit, single bathroom: 10–15 L/min peak. A 10" Big Blue two-stage handles it.
Three-bedroom family home, two bathrooms: 20–30 L/min peak. A 20" Big Blue two- or three-stage is the right size.
Four-bedroom-plus, two-plus bathrooms, washing machine and shower running at the same time: 30–40 L/min peak. 20" Big Blue minimum, three stages preferred. Twin-housing setups (two cartridges per stage in parallel) are an option for very high-flow homes.

Undersizing is the most common mistake. A 10" × 2.5" two-stage system on a four-bedroom home will choke on flow during peak periods and burn through cartridges in months instead of a year.

How to choose

On town water, want softer showers and protected appliances? Two or three-stage 20" × 4.5" whole-house system. Keeps flow up across multiple outlets and only needs cartridge changes once or twice a year.
On rainwater or bore water? Three-stage with UV is the minimum. See the rural tank water page for the full rationale.
Small home, low usage, or holiday house? A 10" × 2.5" two-stage system is cheaper, smaller, and uses widely-stocked cartridges — but watch the rated flow rate, since smaller housings drop flow when two outlets are in use.

Whole-house systems must be installed by a licensed plumber. WaterMark certification is required for any product that connects to mains pressure; every certified product on this site shows its licence number on the page.