Water filter glossary — every term explained plainly

A filter's guarantee that it will stop all particles at or above the stated size. Stricter and more meaningful than a nominal rating. An absolute 1-micron filter will block every particle of 1 micron or larger. Important for microplastic and cyst removal.

The national standards developed by the NHMRC that all Australian water utilities must meet. Set maximum allowable concentrations for hundreds of parameters including bacteria, chemicals, metals and aesthetic factors. Perth tap water meets these guidelines.

A regeneration process used in some whole-home filter systems (typically KDF or catalytic carbon tanks) where water flow is reversed to flush accumulated contaminants out of the filter media. Extends media life. Not required for standard cartridge-based systems.

Industry nickname for the standard 4.5" × 10" or 4.5" × 20" filter housing used in whole-home systems. Big Blue housings accept a wide range of cartridge types from multiple manufacturers, meaning no lock-in to a single supplier's cartridges.

A valve arrangement installed alongside a whole-home filter that allows water to route around the filter for maintenance, cartridge changes or emergencies — without cutting supply to the whole house. A whole-home installation without a bypass valve is a red flag. See our installation guide.

Filter media made from activated carbon compressed into a solid block form. More effective than granular activated carbon (GAC) at removing chlorine, chloramine, taste, odour and fine particles because water must pass through rather than around the media. The standard for Perth whole-home taste and odour treatment.

A standard cartridge fits industry-common housing sizes (e.g. Big Blue 10" or 20") and can be sourced from many suppliers. A proprietary cartridge is designed to fit only one supplier's housing and must be purchased from them. Proprietary cartridges create ongoing cost lock-in and are a major risk factor when choosing a system.

Chlorine combined with ammonia used as a secondary disinfectant in water distribution. More stable than free chlorine over long pipe networks, but harder to remove — requires carbon block with extended contact time rather than standard GAC. Common in Australian mains water.

The primary disinfectant added to Perth and most Australian mains water. Added deliberately to kill bacteria from the treatment plant to your tap. Taste is noticeable above ~0.5 mg/L. Perth mains water typically contains 0.1–0.8 mg/L. A carbon block filter removes it effectively.

Added to most Australian mains water at 0.5–1.0 mg/L to improve dental health, as directed by state health departments. At these levels it is safe. Standard carbon filters do not remove fluoride. Removal requires activated alumina, bone char, or a reverse osmosis system.

Activated carbon in loose granule form. Effective at removing chlorine, taste and odour, but water can channel around granules over time. Less effective than carbon block at fine particles and chloramine. Often used in whole-home pre-filters before a carbon block stage.

The concentration of dissolved calcium and magnesium in water, measured in mg/L CaCO₃. Below 60 = soft, 60–200 = moderate, above 200 = hard. Perth mains water is mostly above 200, and the hardest northern suburbs can exceed 300. Causes limescale on appliances and affects taste. See our Perth hardness guide.

Water Corporation's primary water supply infrastructure serving Perth and surrounding regions. Draws from desalination (~37–47%), groundwater (~39–46%), dams (~11–16%), and groundwater replenishment (~3–8%). The source mix varies by season and rainfall. The high groundwater proportion is the main reason Perth water is hard.

A process where unwanted ions in water (typically calcium and magnesium causing hardness) are swapped for other ions (typically sodium or potassium) using a resin bed. The basis of traditional salt-based water softeners. Increases sodium content of treated water as a side effect.

A copper-zinc alloy filter media that removes heavy metals (iron, lead, mercury), hydrogen sulphide (rotten egg smell), and free chlorine through a redox (oxidation-reduction) reaction. Does not remove PFAS, microplastics, hardness, or bacteria. Often combined with carbon block for broader treatment. Useful for Perth bore water with iron issues.

White or off-white mineral deposits (primarily calcium carbonate) that build up on heating elements, tap aerators, shower screens and inside pipes when hard water is heated or evaporates. Reduces hot water system efficiency by up to 30%, blocks shower heads, and shortens appliance life. A primary reason Perth homeowners install filter systems.

The situation where a filter system uses proprietary cartridges only available from one supplier, giving that supplier control over your ongoing maintenance costs permanently. One of the most financially significant risks when choosing a system. FilterOut scores all suppliers on lock-in risk as one of ten criteria.

One-millionth of a metre. The unit used to express a filter's pore size or particle removal threshold. Human hair is ~75 microns. Most bacteria are 0.2–2 microns. Cryptosporidium cysts are ~4 microns. Microplastics range from 1 µm to 5mm. A 1-micron absolute filter is the minimum for reliable microplastic removal. A 0.2-micron filter is required to physically remove most bacteria.

Plastic particles smaller than 5mm found in tap water, bottled water and human tissue. Removed by carbon block filters rated at 1 micron absolute or finer, or by reverse osmosis. Standard GAC, UV and KDF have no effect on microplastics. See our microplastics guide.

A filter's approximate particle removal threshold — typically meaning it removes around 85% of particles at the stated size, not all of them. Less stringent than an absolute rating. When buying for health reasons (removing cysts, bacteria or microplastics), always look for an absolute rating.

Independent third-party performance certification from NSF International (US-based but recognised in Australia). The number matters: NSF 42 = taste, odour, chlorine. NSF 53 = health contaminants (lead, cysts, VOCs). NSF 58 = reverse osmosis systems and PFAS. Verify any claim at nsf.org. See our certifications guide.

Australia's accreditation body for testing laboratories. If you want independent water testing, look for a NATA-accredited laboratory — this ensures the testing methods and results meet national standards. More reliable than in-home sales demonstrations.

A group of synthetic chemicals used in industrial and consumer products including firefighting foam (AFFF). Called "forever chemicals" because they do not break down in the environment or human body. Linked to health effects at elevated exposures. In Perth, mainly a concern near defence sites. Only removed effectively by NSF 58-certified reverse osmosis. See our PFAS guide.

A filter system installed at the point where the mains water line enters a property, treating all water before it reaches any tap, shower or appliance. Also called a whole-home filter. Contrasts with a POU (Point of Use) filter which treats water at a single tap only.

A filter installed at a single outlet — typically under the kitchen sink — treating only the water at that tap. Provides higher-quality filtration at lower cost than a whole-home system, but does not treat shower water or protect appliances from hardness.

A filtration process that forces water through a semi-permeable membrane with 0.0001-micron pores, removing dissolved solids, heavy metals, PFAS, fluoride, nitrates and most other contaminants. Produces very pure water but wastes 2–4 litres for every litre filtered. Typically installed under-sink. NSF 58 certifies RO systems. Does not require a whole-home installation to be effective for drinking water.

The chemical reaction principle behind KDF filtration. Dissimilar metals (copper and zinc in KDF) exchange electrons with dissolved contaminants, converting them to harmless or insoluble forms. Effective for free chlorine, hydrogen sulphide, and heavy metals.

The first stage in a whole-home system. A physically rated filter (typically 5–50 microns) that removes sand, silt, rust particles and other suspended matter. Protects downstream carbon and KDF stages from premature clogging. Should always be the first stage in any multi-stage system.

Treatment to prevent calcium carbonate (limescale) depositing on surfaces when hard water is heated or evaporates. Can be achieved by physical removal (salt softener via ion exchange) or by crystal modification (TAC, which prevents scale formation without removing minerals). See our TAC vs salt comparison.

A salt-free water treatment technology that transforms dissolved calcium and magnesium into microscopic crystals that cannot adhere to surfaces. Prevents limescale formation without removing minerals from the water and without adding sodium. No salt, no waste water, no electricity. The most cost-effective hardness treatment for Perth homes. See our 10-year cost comparison.

A measure of all dissolved material in water (mainly calcium, magnesium, sodium, potassium and other minerals). Measured in mg/L or ppm. High TDS in Perth mains water is mostly harmless minerals, not contamination. TDS meters cannot detect bacteria, PFAS, pesticides or heavy metals. Often misused in sales demonstrations. See our onsite testing guide.

Disinfection byproducts formed when chlorine reacts with natural organic matter in water. Includes chloroform and similar compounds. Associated with health risks at elevated long-term exposures. Levels in Australian treated water are generally well within ADWG limits. Carbon block filtration is effective at reducing THMs. Covered by NSF 53 certification.

Water disinfection by exposing it to UV-C light, which damages the DNA of bacteria, viruses and protozoa so they cannot reproduce. Does not remove any chemicals, minerals, PFAS, or microplastics. Requires clear (low-turbidity) water to be effective — a sediment pre-filter is essential. Most useful for bore water, rainwater, and rural properties with microbiological risk.

Australia's mandatory certification scheme for plumbing and drainage products, administered by the ABCB. WaterMark certifies that the hardware (housings, valves, fittings) is safe to plumb into a drinking water supply. It does not certify that the filter cartridge removes any specific contaminant. A product can be WaterMark certified and have no NSF performance certification. These are separate questions. See our certifications guide.

A filter system installed on the main water line entering a property, treating all water before it reaches any outlet. Typically multi-stage: sediment → carbon block → KDF or TAC → optional UV. Protects appliances, provides filtered water at every tap and shower. Requires a licensed plumber for installation in Australia.