Filters come in two commercial shapes: a housing you keep with a cartridge you replace, and a sealed unit you throw away entire. The first is almost always cheaper to own and more flexible, provided the cartridges it takes are standard rather than proprietary. Working out which you are buying takes one look at the specification and saves years of unnecessary cost.
Standard cartridges are the thing to look for
The domestic standard is a cartridge described by length and diameter, most commonly ten or twenty inches long in two common diameters. A housing that takes those can be filled with sediment, carbon, catalytic carbon or specialist media from any manufacturer, at competitive prices, for as long as the housing lasts. A housing that takes only the maker's own shaped cartridge locks you into their pricing and their continued existence, which is a real risk over the ten or fifteen years a housing can serve.
What sealed units are actually for
They are not simply worse. A sealed inline unit is compact, needs no housing, cannot be assembled wrongly and has no o-ring to leak, which suits fridges, caravans, hose lines and any position where servicing is awkward. The trade is cost per volume treated and the waste of throwing away a body every time. Where a sealed unit is fitted in an accessible position and used constantly, a housing with replaceable cartridges will usually be cheaper within a year or two.
The parts that decide the housing outlives the cartridges
Buy o-rings with the cartridges, because the seal is the wear part and a hardened o-ring is the cause of nearly every post change leak. Check that spare o-rings and a matching sump wrench are available for the model. Prefer a housing with a pressure release button, which makes opening it far easier. And if it will live somewhere warm, bright or on a hot line, consider whether the material suits, since ultraviolet and heat both embrittle plastic housings over time.
Changing them so the saving is real
The economics only work if cartridges are changed on time, since a cheap cartridge left in for two years is worse than an expensive one changed annually. Write the fitting date on the housing. Change sediment elements on pressure drop where gauges are fitted and carbon on throughput, since exhausted carbon looks identical to new. Buy a spare set with each change so the excuse of not having one to hand never arises. Our replacement filter guide covers matching cartridges to the standard housings.
Questions people ask about replaceable water filters
Are replaceable cartridge filters cheaper?
Usually, provided the housing takes standard sized cartridges rather than proprietary ones. The housing lasts years while only the media is replaced.
When is a sealed unit the better choice?
Where servicing is awkward or space is tight: fridges, caravans, hose lines. It cannot be assembled wrongly and has no o-ring to leak.
What should I buy alongside cartridges?
Spare o-rings and food grade silicone grease. The seal is the wear part and causes nearly every leak found after a filter change.
How do I avoid being locked in?
Check that the housing takes standard length and diameter cartridges before buying, rather than a shape only one manufacturer makes.