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Carbon Block Filters

By Austin Armstrong June 28, 2021

In the water filtration market, there exist many different kinds of filters. For those interested in understanding the market, there is a bit of a learning curve. Even after you internalize how these different systems work, you then have to weigh the cost and utility against performance. If you can manage this, you’ll begin to see that most of these systems are not a good value.

One kind of filter stands out among the others as particularly effective at removing a wide array of contaminants at a high level of efficiency: The Carbon Block Filter. This page discusses this type of filter in detail, exploring how they are made, how they work, and why they are effective. This type of filter is used exclusively by The Water Machine, and is the secret to its ability to reduce concentrations of various contaminants to almost undetectable levels.

What is a Carbon Block Filter?

A carbon block filter is a solid block of carbon that separates two tanks. Assuming the filter’s design prevents any possible leaks from the source tank into the purified tank, that means that all water must pass through the block before it reaches the second tank. Most contaminants will be unable to pass through the carbon block.

How Do Carbon Block Filters Work?

Carbon block filters are typically made of activated carbon, which means that the carbon is processed in such a way that it produces millions of tiny low-volume pores. Although the block is solid, the millions of pores greatly multiply its surface area, like the inside of a sponge. This microporosity dramatically increases the amount of time that the water is exposed to the carbon during filtration.

Activated carbon filters make use of a process known as adsorption. This process removes contaminants in two ways: First, the pores of the carbon block are small enough that many contaminants become trapped while passing through it. Second, other contaminants form a chemical bond with the carbon material inside the filter, and thus become trapped inside.

Carbon block filters have pores that range in size from 0.5 microns to 10 microns, with an average size between 1 and 5 microns. The smaller the pore size, the more contaminants will be filtered out. However, smaller pores also become clogged faster than larger ones.

How Are Carbon Block Filters Made?

The two processes used to manufacture carbon block filters are compression molding and extrusion molding. Each process is described briefly here.

Compression Molding

Compression molding is what it sounds like. Carbon is added to a polymer in separate molds, where the mixture is subjected to heat and pressure. This process continues until the material compresses and hardens. Depending on the size of the carbon and binder mesh, the manufacturer can choose the size of the pores that form within the carbon block. These pores can be as small as .1 microns in diameter, and as large as 20 microns. After the material cools, the blocks are cut into form and added to the other parts to form a filter cartridge.

Extrusion Molding

This process also combines carbon with a polymer to form a carbon block. However, the key difference is that instead of compressing the material into a mold, the material is twisted into a tubular shape. After cooling, these tubular blocks are cut and added to the other parts to form filter cartridges.

Each of these processes has its advantages and disadvantages, and both are used by manufacturers. Compression molding is labor and time intensive, but it does allow for considerable variation in the choice of polymer, and thus it offers considerable flexibility with respect to how the filter performs. Extrusion molding is more affordable, making it more appealing to manufacturers who don’t need as much versatility during the molding process.

Where do they Find the Carbon?

When sourcing carbon to make carbon block filters, a few options stand out. Wood, bituminous coal, and coconut are the current favorites. Wood has a lower cost, and is renewable - sort of. The right trees may be less expensive, but they take a long time to grow. Bituminous coal is affordable and relatively easy to find. However, it can become contaminated more easily than other materials.

Coconut has some significant advantages. The carbon from coconut shells has a large number of micropores, and they are very small. This makes them more effective at trapping certain toxic chemicals, which might slip through pores found in other sources. Coconut also is more pure, leaving less ash from the manufacturing process. It is also a completely renewable resource.

What Contaminants do Carbon Block Filters Remove?

Because the right manufacturer can alter the size of the micropores during the molding process, they enjoy a significant degree of control over what kinds of contaminants the block filter can remove, and how effective the filter is at doing so. Carbon block filters tend to be quite effective at trapping heavy metals, volatile organic compounds (VOCs), pesticides and other pollutants, and water “purification” chemicals added by the municipal water system (e.g. chlorine, fluoride).

Carbon block filters also stand out when filtering microbes, which tend to fall into three categories: Bacteria, viruses, and microbial cysts. The majority of filter brands make no claims about their ability to remove these organisms. That’s too bad, because consumers tend to assume that a filter will meet this most basic standard. But carbon block filters with small enough micropores can even remove viruses, which tend to be between 0.2 and 0.4 microns in size.

What should I look for in a Carbon Block Filter?

There are a few qualities that enable some products to outshine competitors. While it might take a little time to evaluate different products with respect to these different characteristics, it is worth the time. The right product will last for many years in your household, and save you considerable time and expense. It will also have a huge impact on your health.

Filter Efficiency

By far, the most important quality is filtration. If your filter can’t remove the most dangerous chemicals and pathogens to almost non-existent levels, then you might want to consider what your goals are. Health and safety are priority number one, and the best carbon block filters will all but eliminate any health risk your municipal water might have.


Capacity matters in two respects. The system has a capacity for how many gallons of purified water it can hold at any given time. This matters because if the system is gravity-fed, water can take a while to flow through the carbon block. Capacity also references the number of gallons that a filter block can purify before it needs to be replaced. If you’re planning on paying more for a quality carbon block, you should also make sure that it lasts a while. Nobody likes to spend a fortune on replacement filters.


How easy is the system to use? Is it easy to clean? Is it easy to tell when it has become dirty? Many carbon block systems are gravity-fed. These systems are easy to operate, because once they are assembled, all you have to do is refill the upper tank when it becomes low and clean the filter occasionally. Gravity does all the work. Because they don’t require electricity, if you find yourself in a crisis, you will always have clean water, even if you have to fill your system from a contaminated source.


Cost should be your last consideration. Ironically, the more expensive filters are actually the least expensive over time. That’s because they are made with quality materials that don’t need to be replaced. When you evaluate cost, always consider the entire life cycle of the product. This is where many filters reveal themselves as inferior, while others stand out.

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