Almost every water filter comparison leads with the purchase price. It is the least useful number in the decision. Cartridges are where the money goes, and the cheapest system to buy is frequently the most expensive to own.
The arithmetic nobody does
Work it out this way: find the replacement cartridge, note its price, note how many you need per year, multiply. Then add that to the purchase price and divide across five years.
A pitcher at $40 taking cartridges every six weeks costs far more over five years than an under-sink system at $350 taking two cartridges a year. The pitcher looks cheap on the shelf and is not cheap to live with.
Where each type tends to land
Pitchers have the lowest entry cost and the highest cost per litre. Cartridges are small, capacity is limited, and a busy household replaces them constantly.
Faucet mounts sit slightly better — larger cartridges, longer intervals — but the units themselves are not built to last and often need replacing entirely after a few years.
Under-sink carbon is usually the best value over five years for a household that drinks a reasonable amount of water. Higher purchase price, but cartridges last six to twelve months and cost proportionally less per litre.
Reverse osmosis has multiple cartridges on different schedules plus a membrane every few years, so annual cost is higher — and it wastes water, which shows up on a metered bill.
Whole-house has the highest purchase and installation cost but very long cartridge intervals. Per litre of water treated it can be surprisingly reasonable, because it treats everything.
The trap: proprietary cartridges
Some manufacturers design housings that only accept their own cartridges, then price those cartridges accordingly. Before buying any system, check whether replacements are widely stocked and whether third-party equivalents exist. A system tied to a single supplier gives that supplier the ability to raise your running cost whenever they like.
Cost is not the only axis
A cheap filter that only handles chlorine taste is not good value if what you actually needed was lead reduction. Match the certification to the problem first — NSF/ANSI 42 for taste, 53 for health contaminants — then compare running costs among the options that genuinely solve it.
Comparison chart with costs → · Replacement intervals →
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