Every one has an opinion of what is the right set of cartridges. Right? Experience is your proof, but we start you off with a set based on 1000's of owners experiences,

5 Micron (5M) pleated paper element (1st stage)
Normally used in the first filter, taking water directly from the pump or street pipe.
This is a surface element which traps bigger organic particles (dirt, mud, silt, leaf etc), which extends the life of next filter element.
If this element blocks up too quickly (should last 6mths), a coarser (say 20M) element can be substituted.
Pleated Paper elements can be cleaned, using a bottle of filter wash (the lodged material 'easily drops out') which will do 20 washes. Be careful about skin contact with this material which by definition is not healthy.

1 Micron (1M) polypropylene element (2nd stage)
Normally used in the second filter, this is a 'depth' element which fills up from the outside to the inside, and is not cleanable.
When these 'fill up' they block water flow (cause a significant pressure drop).
The primary purpose of this element is to increase the clarity of the water that enters the UV chamber (which needs a turbidity of 7 - which if you fill up a new white 10 litre pale will photograph very clearly). This element also traps many harmful living nasties such as cysts.

Carbon (5M) element (Final stage)
Activated Carbon (or charcoal) is an excellent way to remove odour, muddy taste, and a host of chemicals (such as chlorine, fluoride, pesticides etc). This element is manufactured by heating a solid carbon block to 500deg then cooling it, which creates 'millions' of fractures. This provides an incredible amount of surface area for the passing water to touch. The carbon absorbs the chemicals. However without protection from the 1M element, the Carbons many 'slivered surfaces' will get 'a coating of mud', and therefore will not touch the passing water. We have seen sites where the Carbon has ceased working after just 2 months because it has not been protected by a 1M element.

How many filters do I need?
You must have at least a 1M element to make sure that the water entering the UV chamber has the required clarity for the UV chamber to effectively sterilize the organisms reproductive organs. You need a 5M to take out sediment levels typically in tank water, that will all to quickly block up an unprotected 1M. You need a Carbon to take out chemicals and odor.

•    single filter - no chemicals or odor and very little sediment
•    two filters - no chemicals or odor but sediments present; mildly chlorinated clean water
•    three filters - chemicals and odor and sediments; heavily chlorinated clean water
The Chlorine Story and City Water Standards
Auckland has an A++ standard which is heavily chlorinated, whereas for example Melbourne has a B+ standard with considerably lower chlorine. This is unlikely to change, particularly if the take off from the Waikato river increases.
Clarity or sediment levels will depend where you are. North Shore pipes are new, whereas City side are old and rusty.
A single carbon filter will only remove about 50% of the chlorine, whereas two carbons will raise this to about 80%. Sediments in the water will slick up the carbons if not protected by a 1M. In this situation we advise a 3 filter system (1M, Carbon, Carbon).

UV Water Systems Models
We can supply systems with either 1, 2 or 3 filters. Retrospectively adding a filter is possible, but costly due to the time needed to dismantle the filter set from the backing board, and re-aligning the inlet pipework.
1.    Single Filter System referred to as the Bach System
2.    Two Filter System referred to as the Silver System
3.    Three Filter System referred to as the Gold System
We hope this helps you decide which system will be best for your situation.