Water Filter FAQs
Reviewed by Chris Raven, Auckland Branch Manager, Pumps Online
Choosing the right water filter depends on where your water comes from and what you need to treat. These frequently asked questions explain how UV, carbon, sediment and reverse osmosis systems work, what different filters reduce, and how to maintain your water filtration system.
Choosing a Water Filtration System
What type of water filter do I need?
The right water filter depends on your water source and the issue you want to address. Sediment filters reduce particles such as dirt and grit, carbon filters reduce chlorine and improve taste and odour, UV systems inactivate microorganisms, and reverse osmosis systems reduce many dissolved contaminants.
Before choosing a system, identify whether your water comes from a tank, bore or town supply and what you want the treatment system to achieve.
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What is the difference between a whole-house filter and an under-sink filter?
A whole-house filtration system treats water as it enters the home, while an under-sink filter treats water at a specific tap. Whole-house systems are suitable when you want to treat water throughout the property. Under-sink systems focus on drinking and cooking water from one outlet.
The right option depends on your water source, household needs and the contaminants or water-quality issues you want to address.
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What contaminants do whole-house water filters remove?
Whole-house water filters reduce different contaminants depending on the cartridges installed. Sediment filters primarily reduce dirt, grit, silt and other particles. Carbon filters can reduce chlorine and improve taste, smell and colour.
Tank and bore water may require sediment filtration and UV disinfection, while town-supply water may use carbon filtration to reduce chlorine. The correct combination depends on the water source and treatment goal.
What is the best filter for rural tank water?
Sediment filters are commonly used as the first stage of rural tank-water filtration. Pleated and polyspun cartridges are available in micron ratings ranging from 50 microns for larger sediment down to 1 micron for finer particles.
If tank water is used for drinking, sediment filtration alone may not be enough. Depending on the water quality and system, it may also require UV disinfection or another suitable treatment method.
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Is UV water treatment necessary in New Zealand?
UV treatment is commonly recommended for untreated water sources that may contain harmful microorganisms, including tank, bore, creek, river, stream and well water. It is not normally required for a compliant town water supply.
The correct treatment depends on the water source, water quality, flow rate and intended use. Seek advice before selecting a UV system for drinking water.
UV, Carbon and Sediment Filters
Does UV remove bacteria from water?
No. UV treatment does not physically remove bacteria from water. It uses ultraviolet light to inactivate bacteria and other microorganisms, preventing them from reproducing and causing illness.
UV effectiveness depends on correct sizing, flow rate, installation, maintenance and water clarity. UV does not remove sediment, dissolved chemicals, taste or odour, so it is commonly used with appropriate pre-filtration.
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What is the difference between UV and carbon water filters?
UV and carbon systems perform different jobs. UV treatment inactivates harmful microorganisms, while carbon filtration reduces chlorine and can improve the taste, smell and colour of water.
UV is commonly used for tank and bore water. Carbon filters can be used for town or tank water. Some treatment systems combine UV, sediment and carbon filtration to address several water-quality issues.
Does a carbon filter remove chlorine?
Yes. A suitable activated carbon filter can reduce chlorine and the associated chlorine taste and odour in water. The level of reduction depends on the carbon type, filter capacity, flow rate, contact time, water quality and condition of the cartridge.
Carbon block, granular activated carbon and KDF-GAC filters are commonly used for chlorine reduction. Choose a filter that is designed and tested for the intended application.
What water filter removes chlorine?
Carbon block, granular activated carbon and KDF-GAC filters are commonly used to reduce chlorine. The best option depends on your water source, system size, flow rate and the amount of water being treated.
A filter's micron rating describes the size of particles it is designed to capture. It does not, by itself, show how effectively the filter reduces chlorine.
What is the difference between carbon and sediment filters?
Sediment filters capture particles, while carbon filters address chlorine and selected taste, odour and colour issues. Sediment filters are commonly used to reduce dirt, grit, silt and debris. Carbon filters use adsorption to reduce chlorine and certain other substances.
Many filtration systems use both because each filter performs a different role.
What is a micron rating on a water filter?
A micron rating indicates the size of particles a filter is designed to capture. One micron is one-thousandth of a millimetre. The lower the micron rating, the finer the filtration.
- A 50-micron filter captures relatively coarse sediment.
- A 20-micron filter captures larger dirt and grit.
- A 5-micron filter captures smaller particles.
- A 1-micron filter provides finer particle filtration.
When buying a replacement cartridge, check the micron rating and dimensions of the existing filter to ensure the replacement suits the system.
Reverse Osmosis
What Is a Reverse Osmosis Water Filter?
A reverse osmosis water filter is a multi-stage water filtration system designed to reduce contaminants at a molecular level.
Unlike basic filters, reverse osmosis systems can reduce:
- Dissolved salts and minerals
- Chlorine and chemical tastes
- Some heavy metals (e.g. lead, copper)
- Sediment and fine particles
How does reverse osmosis work?
Reverse osmosis uses water pressure to push water through a very fine membrane. Water molecules pass through the membrane while many dissolved minerals and contaminants are separated and flushed away.
A typical underbench reverse osmosis system uses a sediment pre-filter, carbon filtration, an RO membrane and a storage tank. The treated water is then delivered through a separate drinking-water tap.
Most systems follow a four-stage process:
- Sediment Filtration
- Removes dirt, rust, and larger particles.
- Carbon Filtration
- Reduces chlorine, taste, and odour before water reaches the membrane.
- Reverse Osmosis Membrane
- Reduces dissolved solids and microscopic contaminants.
- Post-Carbon Filtration
- Final polishing stage to improve taste.
Filtered water is typically stored in a pressurised tank, ready for use when needed.
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Do I need a reverse osmosis system?
You may need reverse osmosis if testing identifies dissolved contaminants that other filters are not designed to reduce. Depending on the system and its tested performance, underbench RO can reduce fluoride, nitrates, arsenic and certain heavy metals.
RO also reduces naturally occurring dissolved minerals, including calcium and magnesium. Identify what is in the water and check the treatment claims for the specific RO system before choosing one.
What Are the Benefits of Reverse Osmosis Water Filters?
Reverse osmosis water filters provide high-level drinking water filtration by reducing many dissolved impurities. They can improve taste and odour, deliver filtered water through a dedicated tap, fit neatly beneath the kitchen sink and provide consistent filtration for everyday household use.
- High-Level Filtration: Reduces many dissolved impurities that standard filters may not address.
- Improved Taste and Odour: Carbon stages help reduce chlorine and unpleasant smells.
- Convenient Daily Use: Delivers filtered drinking water directly from a dedicated tap.
- Compact Installation: Most residential systems fit beneath the kitchen sink.
- Reliable Performance: Provides consistent filtration for everyday drinking and cooking water.
Water-Quality Problems
Why does my water still smell after filtration?
Water may still smell if the installed filter is not designed to treat the source of the odour, the filter needs replacing, or the smell is coming from the plumbing, drain or hot-water system.
The cause depends on the water source, filter type, system configuration and where the smell occurs. Check whether the smell affects one tap or every tap, and whether it occurs in hot water, cold water or both, before changing the treatment system.
Why is my UV light on but my water still smells bad?
A working UV light does not remove water odours. UV treatment targets microorganisms, while taste and smell are normally addressed by other treatment methods, such as a suitable carbon filter.
The carbon cartridge may need replacing, or the system may not contain the correct filter for the cause of the smell. UV lamps normally operate continuously and should be replaced according to the manufacturer's schedule.
Why does tank water suddenly smell after rain?
Heavy rain can stir up sediment, debris and other material at the bottom of a water tank. Rain can also carry new material from the roof and gutters into the collection system, causing a noticeable change in smell.
A suitable carbon filter may help reduce some odours, but the tank may also require inspection, cleaning or an appropriate tank-water treatment. The correct response depends on the cause of the smell.
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Why does bore water smell?
A sulphur-like or rotten-egg smell in bore water may be associated with hydrogen sulphide or sulphur-reducing bacteria. Other water-quality characteristics may also affect bore-water taste, smell or colour.
An odour alone cannot identify everything present in the water. Testing is the best first step before selecting a filtration or treatment system.
Why does my water taste metallic?
A metallic taste may be caused by iron in the water or corrosion from copper or iron plumbing. If the taste is chlorine-like rather than metallic, chlorine in a town water supply may be the cause and a suitable carbon filter may help reduce it.
If the taste persists, test the water or seek professional advice before selecting a filter.
What water filter removes iron?
The correct treatment for iron depends on the form and concentration of iron in the water. Solid or oxidised iron can often be removed through filtration. Dissolved iron may require oxidation or another treatment stage before it can be filtered. In some situations, a water softener may reduce dissolved iron.
Have the water tested first so the iron level and type can be identified before selecting a treatment system.
Filter Maintenance and Replacement
How often should water filters be replaced?
Water-filter replacement frequency depends on water quality, water use, cartridge type and the manufacturer's instructions. As a general guide, 10-inch whole-house jumbo filters may last 6–12 months, 20-inch jumbo filters may last around 12 months or longer, and standard underbench filters may last 3–6 months.
Replace a filter sooner if performance declines. If cartridges regularly block within three months, investigate the water quality and filtration setup.
What are the signs that a water filter needs replacing?
Three common signs that a water filter may need replacing are:
- A noticeable reduction in water pressure.
- A cartridge that is discoloured, slimy or full of debris.
- Changes in water taste, smell or colour, or chlorine becoming noticeable again.
Check the filter first if pressure drops significantly, and always follow the replacement schedule for the specific cartridge.
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Need Help Choosing a Water Filter?
The right filtration system depends on your water source, water quality, flow requirements and what you want to treat. Contact Pumps Online with information about your current system and water source for help selecting a suitable option.