Different filters do different jobs.

The right combination depends on your water source, what’s in the water and how much your household uses.

Here’s a straightforward guide to filter sizes, cartridge types and UV disinfection.

What size system do I need?

Start with your peak flow - the amount of water you might use with several showers, taps and appliances running at once.

Your system needs to handle that demand while providing effective treatment and maintaining useful pressure.

Water quality matters too. A supply carrying more sediment may need additional pre-filtration or greater cartridge capacity.

Standard and jumbo sizes

These are nominal sizes. Check the exact dimensions and compatibility before ordering replacements.

Jumbo housings are also commonly called “Big Blue”, although the housing itself may be another colour.

A larger cartridge generally offers more capacity and can help reduce pressure loss at a given flow. However, the cartridge type, micron rating and condition all affect performance.

Size alone does not tell you the system’s treatment capacity. Check the recommended flow rate for the complete system.

How many filter stages do I need?

Each stage should have a purpose.

A system might include sediment filtration followed by carbon for taste and odour. A supply with heavier sediment may benefit from a coarse sediment stage followed by a finer one.

If UV is included, the filtration must prepare the water to meet the UV unit’s water-quality requirements.

Two or three housings can both be appropriate. The right arrangement depends on your source water and the equipment specifications.

Sediment filters

Sediment filters capture particles such as sand, silt and rust. They are commonly the first stage in a system.

PP spun filters use layers of polypropylene fibre to trap particles. They are replaced when required rather than washed.

Pleated filters provide a large filtering surface. Some are designed to be cleaned and reused; others are disposable. Follow the manufacturer’s instructions for the particular cartridge.

What does “micron” mean?

A micron is a measurement of size. A lower micron rating generally means the filter captures smaller particles.

For example, a system may use a 20-micron cartridge before a 5-micron cartridge, allowing the first stage to catch larger particles.

Check whether the rating is nominal or absolute—these describe different levels of particle-removal performance.

An ordinary sediment cartridge should not be assumed to make water microbiologically safe.

Carbon filters

Activated carbon is commonly used to reduce chlorine taste and odour and improve the taste of water.

It works mainly through adsorption, where substances attach to the carbon’s surface.

Carbon block

Carbon is formed into a solid cartridge. Depending on its rating, a carbon block may also capture fine particles.

Granular activated carbon

Loose carbon granules provide another form of carbon treatment. Performance depends on the media, cartridge design, flow rate and contact time.

Neither type is automatically better for every application, and there is usually no need to install both unless the system has been designed that way.

Ordinary carbon filters do not remove dissolved salt, soften water or reliably remove fluoride. Claims for other contaminants must be supported by the particular cartridge’s specifications.

Do filters remove fluoride?

Standard sediment filters, ordinary carbon filters and UV disinfection do not remove fluoride.

If fluoride reduction is your goal, you need treatment specifically designed for it.

Reverse osmosis - often called RO - can reduce fluoride and other dissolved substances. It is commonly used at a dedicated drinking-water tap.

Specialist fluoride-removal media are also available. Always check the system’s tested reduction claims, operating requirements and replacement schedule.

A filter advertised as removing chlorine should not be assumed to remove fluoride.

Ion-exchange resin

Different resins are designed for different jobs.

Water-softening resin reduces hardness by exchanging calcium and magnesium for sodium or potassium. It does not disinfect water.

Deionising resin removes a broader range of dissolved ions and is commonly used where demineralised water is required. It is different from ordinary water softening.

Choose the resin for the specific water problem. Replacement or regeneration depends on its capacity and the water being treated.

KDF media

KDF is a copper-and-zinc treatment medium used in some cartridges to reduce chlorine and certain dissolved metals.

Its capabilities depend on the grade of media and the system design. Check the product’s specific claims - it is not a general solution for every chemical or a substitute for appropriate disinfection.

Where does UV fit in?

UV uses ultraviolet light to inactivate microorganisms. It works alongside filtration, addressing a different part of water treatment.

For rainwater, bore and surface-water supplies, the system must be selected to suit the source and its risks.

Choose UV by performance - not wattage alone

The important details are:

• The unit’s rated flow at the required UV dose.

• The quality and UV transmittance of the incoming water.

• The manufacturer’s pre-filtration requirements.

• Whether monitoring, alarms or automatic shut-off are needed.

A 55-watt lamp does not, by itself, tell you how much water the system can effectively disinfect.

Sediment, colour and deposits on the quartz sleeve can interfere with UV treatment. Suitable pre-treatment and regular maintenance are essential.

UV does not remove dissolved chemicals, salts or fluoride, and it does not provide ongoing protection against contamination after the water leaves the unit.

If your water supplier issues a boil-water notice, follow its instructions. Do not assume your home filter or UV system means the notice does not apply to you.

When should filters and UV lamps be replaced?

Follow the replacement schedule for your particular equipment.

Cartridge life depends on water quality, usage and the cartridge’s capacity. Reduced flow or increasing pressure loss can indicate a blocked sediment filter, but appearance alone cannot confirm that a cartridge is still effective.

Carbon can lose its treatment capacity without looking dirty.

UV lamps also lose useful output over time, even when they still glow. Replace the lamp and clean the quartz sleeve as the manufacturer directs.

Need help choosing?

Send us your water source, household demand, any water-test results and photos of your existing system.

We’ll help you choose the right filter sizes, cartridge combination and UV system for your application.

Call 09 294 7555 or email sales@pumpandpurify.co.nz.

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