Cartridge life is a manufacturer figure published in litres, and across the shelf it varies by more than an order of magnitude. It is the single number that decides what a filter costs to run, and it is the one most listings put last.
What the figure means
A maker states a rated capacity in litres: the service life it claims for the element before replacement. Like the micron rating and the stated flow rate, it is a manufacturer specification rather than a measurement made to a shared standard, so it is quoted here as the maker publishes it, in the maker’s own unit.
The spread is the striking part. Two cartridges of the same nominal pore size, sold for the same kind of walking, can be rated hundreds of litres apart. A hollow-fibre element quoted in the thousands of litres and a compact element quoted in the hundreds are not variants of one product; they are two different purchases with two different running costs.
Why it decides the price rather than the sticker
The useful arithmetic is division, not comparison. Take what a replacement cartridge costs and divide it by the litres the maker publishes for it. That gives a cost per litre, and it reorders the shelf immediately — a cheap filter with a short-lived element is frequently the expensive one over a season, and an expensive housing with a long-rated cartridge frequently is not.
This also settles the question of whether a proprietary cartridge matters. It does, because a housing that only takes one maker’s element ties the running cost to that maker’s spare part for as long as you own it. Check that the spare is listed and available before you commit to the body.
Litres are not the only limit stated
Several makers publish a time-based interval alongside the litre figure — a period after which the element should be replaced whatever the count says. Where both appear, both are the manufacturer’s instruction, and the earlier of the two is the one that applies.
Storage matters as much as usage. Instructions cover how an element should be dried or kept between trips, and they cover freezing, which is what ends more cartridges early than the stated litres ever do. An element that has frozen cannot be assessed by looking at it, and the maker’s guidance is the only sound answer to what to do next.
Flow falls long before the litres run out
A cartridge does not deliver its stated flow rate all the way to its last litre. Flow is measured on a clean element and falls as the element loads, which is why makers supply a backflush syringe or coupling and state how often to use it. Neglect that and the filter becomes unusable well inside its rated capacity, with the counter nowhere near the published figure.
So the two numbers describe different things: the flow rate describes the experience of using it, the capacity describes how long you own it for. Neither is a substitute for the other.
Keeping the boundary clear
A capacity in litres tells you how long the maker says the element is intended to be used. It is not a statement about the water going through it, and neither is anything else on the specification sheet.
Whether water from a particular source is fit to drink is not a question a rating answers. It belongs to the manufacturer’s instructions, which state what the product is intended for, and to the local authorities responsible for water in the place you are standing. This site reports what makers publish — the pore size, the flow, the litres — and leaves that decision where it belongs.
The manufacturer's own instructions come first, and this page does not stand in for them. Every weight, packed length, hydrostatic head, denier, micron rating, lumen figure and temperature on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A weight is reported as the maker counts it, and is never restated as another kind of weight, because the two are not the same figure. And the second statement repeated rather than assumed: nothing on this site tells you that water is safe to drink. A filter reduces what its manufacturer declares it reduces, down to the micron rating that manufacturer publishes, for the cartridge life that manufacturer publishes. Whether a given source is drinkable is a matter for the maker's own instructions and for the local authorities, and it is never answered here.
What people ask before buying
What happens when a cartridge reaches its stated litres?
The manufacturer's instructions say what to do, and they are the only source worth following on it. Some elements simply stop passing water at a usable rate; others carry a stated replacement interval in time as well as in litres. Read both figures on the packaging.
How do I keep track of the litres I have put through?
Count containers rather than litres. If you know the capacity of the bottle or pouch you fill from, a tally of fills is close enough to compare against a figure quoted in the thousands, and it is the only practical method in the field.
Last reviewed 6 September 2026