How to Choose a Water Filter Cartridge
Three things decide which cartridge you need: the size your housing takes, the micron rating you want it to filter to, and the type of media.
Get the size wrong and it will not fit. Get the micron wrong and you will either not fix the problem or you will be changing cartridges every few weeks. Here is how we pick them.
The short answer
Decided by your housing, not by you. Measure the old cartridge or read the housing label before ordering.
Smaller number, finer filtration. Smaller is not better. Stage it instead: coarse first, fine behind it.
On tank or bore water, sediment first, carbon second. Carbon is the expensive stage, so it goes behind sediment.
1. Size is decided by your housing, not by you
Puretec cartridges come in two diameters and two lengths, and the code on the old cartridge tells you which you have.
- Slimline is the standard 2.5 inch diameter. Code ends in 1 for 10 inch or 2 for 20 inch.
- Jumbo, which Puretec calls MaxiPlus, is 4.5 inch diameter. Code ends in MP1 for 10 inch or MP2 for 20 inch.
So a PL10MP1 is a Pleated cartridge, 10 micron, in the 10 inch Jumbo size. A PX051 is Polyspun, 5 micron, 10 inch Slimline.
Jumbo holds roughly four times the media of slimline, so it passes more flow and holds far more dirt before it blocks. That is why whole house systems use it and under sink systems do not.
If you are choosing a new system rather than replacing a cartridge, this is the decision that matters most: a jumbo housing costs more once, and saves you cartridge changes for the life of the system.
Measure the old cartridge or read the housing label before ordering. If you are stuck, photograph the housing and email it to us.
2. Micron rating: what actually gets removed
The micron number is the size of particle the cartridge stops. Smaller number, finer filtration.
| Rating | Stops | Typical use |
|---|---|---|
| 100, 50, 30 micron | Leaf matter, grit, coarse sand, insects | Coarse pre-filter on dam, creek or very dirty tank water, or ahead of irrigation |
| 20 micron | Visible sediment, fine grit, most tank debris | The usual first stage on roof and tank water |
| 10 micron | Silt, rust, fine sand | General purpose, and the standard grade for dual purpose cartridges |
| 5 micron | Fine silt, rust, sediment you can see in a glass | The most common single sediment stage. Standard on town supply |
| 1 micron | Very fine silt, most visible cloudiness | Polishing stage after something coarser, or ahead of UV |
| 0.5 micron | Cryptosporidium and giardia cysts | Carbon block grades where cyst removal matters |
| 0.35 micron | The finest sediment grade Puretec make | Final polish ahead of a UV steriliser |
3. Smaller is not better
This is the single most common mistake we see, and it is an expensive one.
The wrong way
Fit a 1 micron cartridge as the only filter on tank water and it will block within weeks. Your pressure falls away, the pump works harder, and you are buying cartridges constantly.
The cartridge is not faulty. It is doing exactly what a 1 micron cartridge does when you ask it to catch everything.
The right way
Stage it instead. Put a coarse cartridge first to take the bulk out, then a fine one behind it to polish.
The coarse cartridge is cheap and protects the expensive one. Both last far longer than either would on its own, and your pressure stays where it should be.
Carbon goes second
The same logic applies to carbon. Carbon is the expensive stage, so on tank or bore water it goes second, behind sediment. Put carbon first on dirty water and you throw away good carbon clogged with grit.
4. Which type of cartridge
Five series cover the job. PX and PL are sediment. CB and MC are carbon, for chlorine, taste and odour. DP does sediment and taste in one cartridge, where you only have one housing.
Fit one carbon cartridge or the other, not both.
| Series | What it is | Use it for |
|---|---|---|
| PX Polyspun | Graded density spun polypropylene. Coarser outside, finer inside, so the whole depth loads up | The low cost sediment workhorse. Not washable, replace when loaded |
| PL Pleated | Pleated media, far more surface area in the same housing | Sediment where you want longer life or a washable cartridge. The widest micron range, 0.35 to 100 |
| CB Carbon Block | Bonded activated carbon, most grades with SilverPlus bacteriostatic treatment | Chlorine, taste and odour. Specialist grades for cysts, chloramine and heavy metals |
| MC Moulded Carbon | Moulded carbon, same job as CB | The alternative to CB. Fit one or the other, not both |
| DP Dual Purpose | Carbon impregnated pleated media | Sediment and taste in one cartridge, where you only have one housing |
5. Standard setups
Watch it done
Find your water source below.
Town water, taste and smell the problem
One carbon block, 5 or 10 micron. That is usually the whole job. If your supply is dosed with chloramine rather than free chlorine, use the chloramine reduction grade, because ordinary carbon struggles with it.
Roof or tank water, whole house
Two stages. A 20 micron pleated or polyspun first to take out grit and debris, then a 5 or 1 micron behind it. Add carbon as a third stage if you want the taste improved.
Tank or bore water with UV
Sediment stages as above, finishing at 1 micron or finer before the UV. This is not optional. UV only kills what the light can reach, and cloudy water shields bacteria from it. If you run UV, the fine sediment stage is part of the steriliser, not an extra.
Bore water
Start with a water test. Bore water varies enormously and iron, manganese and hardness are not sediment problems, so no cartridge alone will fix them. We would rather tell you that before you buy than after.
Dam or creek water
A coarse 50 or 100 micron pre-filter ahead of everything else, or you will be changing the good cartridges constantly.
Not sure?
Tell us your water source and what you are trying to fix, and photograph the housing if you are replacing a cartridge. We install this gear around Waihi and Thames every week, so it is usually a two minute conversation. A real person picks up.
