Is your filter system
big enough?

Two things happen. First, you'll notice reduced water pressure whenever multiple fixtures run simultaneously — the filter housing becomes the bottleneck in your plumbing. Second, and less obviously, water moves through the filter media too quickly at high flow rates, reducing contact time and therefore the effectiveness of each filtration stage. This is particularly important for carbon block (chlorine removal) and TAC scale prevention media, both of which have minimum contact time requirements to work properly.

A 15" × 4.5" filter housing is typically rated at approximately 15 L/min maximum flow. A typical family home with 3–4 people, 2 bathrooms and normal morning routines can easily demand 25–30 L/min at peak — two WELS-rated showers at 9 L/min each plus a washing machine fill at 10 L/min is already 28 L/min. A 15" housing simply can't pass that volume without significantly reducing pressure. The standard 20" × 4.5" Big Blue format handles 20 L/min, which covers most 3–4 person households adequately, and is the global industry standard format used by every major filter manufacturer.

No. Size for the busiest realistic minutes of your day — not theoretical maximum simultaneous use. Think about your actual morning or evening routine. For most Perth households that means 2–3 fixtures running at once: two showers and a washing machine, or one shower plus the dishwasher and a basin. You don't need to account for every tap in the house running simultaneously — that never happens in practice. The goal is to have 20–30% headroom above your realistic peak, not to handle an unlikely worst case.

Yes, each additional stage adds pressure drop — typically 15–25 kPa per housing at normal flow rates, more as flow increases. A 3-stage system on Perth's 400 kPa inlet pressure will typically deliver 330–350 kPa at the outlet under moderate flow. This is well above the 200–250 kPa needed for comfortable shower performance. Where it becomes noticeable is at peak demand in undersized systems — high flow rate multiplies the pressure drop across each stage. This is why sizing the housing correctly matters more for 3-stage systems than for single-stage setups.

Most Perth residential homes use 20mm copper pipe for the mains supply, which can theoretically carry 30–35 L/min at safe velocities (1.5–2.0 m/s per AS 3500). This means the pipe itself rarely limits flow in practice — the filter housing is usually the constraint for whole-home systems. Older Perth homes built before the 1980s may have 15mm copper runs internally, which reduce effective flow to around 15–20 L/min, making filter sizing less critical but also making high-flow showers generally impractical regardless of filtration.

Yes — in most cases. The filter housings need to be replaced (different sizes use different mounting brackets and connections), but the pipework leading to and from the filter location and the installation point itself can usually stay in place. For most Perth homes it's a single-visit job. The result is a standard 20" × 4.5" Big Blue format where replacement cartridges are available from any filtration supplier — no proprietary lock-in. See our systems page for our upgrade service.