While a pitcher, in-line system, or other filter vessel is a one-time purchase, most filter parts (the bits actually doing the filtering) have a limited lifespan. So, they’ll need replacing at some point. This makes buying a water filter a process of weighing up the short and longer-term costs—how much are you paying upfront, versus how much will replacement filter cartridges set you back over time?

A key part of that conversation is how long water filters last. The longer you can rely on a filter cartridge to provide you with purer water, the less you’ll be spending on replacements, and therefore, the wider range of filter types you can consider. Here are our estimations of the lifespans of the most popular filter cartridges!

Total Dissolved Solids (TDS)

Perhaps it’s obvious, but for all filters, the biggest determinant of lifespan is the quality and amount of water being filtered. All water that isn’t distilled contains some amount of dissolved solids. As the Government of Canada guidelines describe, the most common dissolved solids (TDS) are:

“Inorganic salts and small amounts of organic matter…calcium, magnesium, sodium and potassium…carbonate, bicarbonate, chloride, sulphate and, particularly in groundwater, nitrate (from agricultural use).”

Depending on where you’re located, your drinking water will benefit from some level of filtering. 500 mg/L or less of Total Dissolved Solids (TDS) has been established as a good marker for safe and palatable drinking water. At higher levels, hardness, unpalatability, mineral deposition and pipe corrosion can occur.

However, you probably don’t want to get rid of everything that’s dissolved in your water. A TDS amount of 300 mg/L or less is considered desirable in terms of taste—with different mineral combinations contributing to the somewhat distinctive flavor of springwater. With more powerful filters, such as reverse osmosis mechanism, you can actually bring TDS levels down to near zero, so it’s definitely worth considering whether this is something you actually want to do.

Filter gallons of water with a high level of sediment per day, and you can expect to cut the life of a filter by half, or more, compared with filtering modest amounts of low TDS water.

Activated Carbon Filters

Activated carbon filters by adsorption. Soluble organics within water (or air) are attracted and bonded to the carbon’s surface, as the solution passes through the filter. Activating carbon means maximizing its surface area, which increases its adsorptive capacity via a process of oxygenation or chemical treatment.

Because a carbon filter works by adhering contaminants to its surface, the filtering component will have a lifespan, becoming less effective as more materials build-up on its surface. The length of that lifespan depends on a couple of factors, including the size of the filter, the quality of the ‘activating’ process, and whether carbon is the sole filtering component. Eventually, a carbon filter will reach its capacity, and become ineffective.

Pitcher filter cartridges

How long do filters last? 3-6 months / every ~80 gallons

Activated carbon pitcher filters (Brita filters and most common filter models) last between three and six months, when used once or twice per day on a regular mains water supply. Brita estimates that their pitcher filters will need replacing every four months or so, if you drink around eleven glasses of water per day.

Faucet-mounted cartridges

How long do filters last? 2-4 months / every ~100 gallons

Because these filters save space by adhering directly to the tap, cartridge filters need to be smaller. This ups their convenience, but normally reduces their lifespan. Expect a faucet-mounted filter to work for around three months.

A carbon water filter cartridge

Other Filter Options

Carbon filters aren’t the only game in town. While they may be the most widely adopted filtering mechanism, more permanent types of filter—such as under-sink or countertop models—often make use of more technical and powerful filter mechanisms. While they may filter water differently, all of the filter types below are capable of removing particles smaller than carbon, such as bacteria and disease-causing microbes.

Also, activated carbon filters can last for a year or longer if they make up one part of a wider water purification system, such as the options below.

Reverse Osmosis replacements

How long do filters last? 1-3 years for membranes

Reverse osmosis refers to the pushing of water through a super-fine, semi-permeable membrane, which catches tiny pollutants and leaves water with a very low TDS. Estimating the lifespan of RO filter systems is a little complicated, due to the fact that most are combined with several other stages (usually carbon filters). However, expect to change RO membranes yearly in hard water areas, and up to between three and five years for use with softer water.

Ceramic cartridges

How long do filters last? Indefinitely (with cleaning)

A traditional and historic filtering mechanism, ceramic filters work in a similar way to activated carbon, by relying on the tiny pores in a ceramic surface to catch bacteria and sediment. Unlike carbon cartridges, however, ceramic filters can be cleaned to increase their lifespan. When water flow begins to slow down, it’s time to clean the filter with a scouring pad or brush—not soap.

UV filter lifespans

How long do bulbs last? 1 year / ~9000 hours of purifying

UV filters offer a different proposition from carbon, RO, and ceramic mechanisms, as they’re designed to destroy harmful pathogens in water, rather than filter anything out. As a result, UV filters are normally installed alongside a carbon or RO component, as well as being long-lasting.

Expect a UV bulb to need replacing yearly, or after around 9000 hours. At this point, a UV Lamp is likely to be functioning at around 60% effectiveness compared to a brand new lamp.

Note: while you may be a lot bigger than a piece of algae, UV light will still harm you. Never work with active UV filters without protective clothing and eyewear.

Summary

It’s worth repeating that estimating the lifespan of a filter is, at best, a case of guesswork based on how much a filter is used, and the level of Total Dissolved Solids existing in the water source.

While most manufacturers will provide a lifespan guide on the product/packaging itself, the only way to truly discover how long a water filter will last is to pay close attention to your first round of usage, and draw conclusions from there.

In other words, if you find that your filter lasts for four months when used in a three-person household in a hard water area, you can feel confident in predicting a decrease in lifespan if you add another person, or an uptick if you move to a soft water area.