When to Change Your Activated Carbon Filter (And Why You Have To)

One of the only costs associated with water purifiers (non-electric) is the replacement of the filter cartridges within those purifiers. Changing the activated carbon is an important part of filter maintenance that will extend the life of your filter and ensure you are getting a clean, toxin-free product every time.

Why You Have to Change Activated Carbon Filters

To understand why you need to change your carbon filter, you’ll need to understand how activated carbon filters work to remove contaminants from water. This is a process called adsorption (not to be confused with absorption). When a sponge absorbs water, the water fills in the holes throughout the sponge. When carbon adsorbs contaminants like chlorine, the molecules, ions or atoms from the chlorine collect like a film on the carbon. That film is called an adsorbate and it is the reason why you need to change your activated carbon filters regularly.

absorption vs adsorption

Absorption (a) and adsorption (b) mechanism. Blue spheres are solute molecules. Source: File:Absorbimento e adsorbimento.svg, commons.wikimedia.org, Author: Daniele Pugliesi

There is only so much space for the adsorbate to collect on the carbon. Once all that space is covered with the pollutant film, the carbon can no longer do its job effectively. In fact, if left too long, an activated carbon filter can start to release certain pollutants in favor of other ones that are more attracted to the adsorption site. This is why it’s so important to change your filter in a timely manner.

When to Change Your Carbon Filter

The question of why you have to change a carbon filter has a very clear answer. The question of when to change the filter is a little more complicated.

There are several factors to consider when deciding how long a carbon filter will last before it needs to be replaced. These factors include:

The quality of your carbon filter

High-quality, well-made activated carbon filters will last longer than shoddy, cheap filters.


Low quality coal filter blocks

A low quality filter lasts much shorter.

The amount of contaminants in your water

A filter will need to be changed with more regularity if it’s filtering water that has a lot of contaminants. The adsorbate will grow faster, requiring a new filter more often.


The volume of water being filtered

A filter used to treat 100 gallons of water each week will last longer than a filter used to treat 500 gallons of water each week.

water used

The manufacturer’s recommendation

The manufacturer of your activated carbon filter will provide you with a guideline for how often you should change your activated carbon filter. This advice can provide a good starting place, but your usage habits will determine exactly how long the filter works at optimum performance before it needs to be replaced.

This wide array of factors means that the question of when to change your water filter will have a different answer for most people and businesses.

Signs Your Activated Carbon Filter Needs to Be Changed

While the durability of your filter will depend somewhat on how heavily it is used, there are some symptoms that will signal when a change is necessary. If the water that comes through the filter starts to take on an unpleasant smell or flavor, this is a sign that your filter is long past replacement time. Additionally, a clogged filter might cause a decrease in water pressure. With activated carbon filters, you’ll never have a visual cue that tells you it’s time for a replacement: the only signals will be smell, taste and (potentially) pressure.smelly water

That said, it’s best not to wait until these symptoms appear. Instead, get on a regular schedule for switching out your old filters with new ones and stick to that schedule. If you’re really unsure about when to change your filter, consult your manufacturer and provide them with a brief overview of your usage habits. They can provide you with appropriate guidance.

Is it time to change out your activated carbon filter? Check out this post with directions for installation and replacement of your carbon block.