Guide to Water Filtration Methods

With the growing number of contaminants found in our water, understanding the different types of water filtration is more important than ever. The delicate interplay between regulation and political and industrial pressure, as well as the ever-changing quality of water due to weather and environmental factors, make it critical for homes and businesses to protect themselves with water filters.

Research has shown bottled water is often subject to less regulation than tap water, so drinking it leaves you vulnerable to impurities at the water’s source. Additionally, the cost of bottled water can be higher than gasoline. The best option for safe drinking water — regarding both safety and cost — is to fill your bottle with water from a home water filtration system.

There are several water filtration methods, each with different strengths. In this article, we will review some of the most popular: carbon block filters, granular activated carbon, reverse osmosis and distillation. We will evaluate the relative strengths and weaknesses of each filtration system, how each one works, how affordable it is and how effectively it filters your water.

Method 1: Carbon Block Filters

Carbon block filters are highly effective at removing contaminants, odors and tastes from water via the use of activated carbon. This type of carbon has a high degree of porosity in its granules, making it able to adsorb more contaminants due to its increased surface area. This gain in surface area is the key advantage of activated carbon. To get an idea of this surface area, consider the fact that one pound of carbon contains an incredible 125 acres of surface area.

Carbon Block Filters

The key distinguishing feature of carbon block filters is the size “mesh” that the carbon creates. Carbon blocks can contain particles that are between 0.045 mm and 0.18 mm. This makes them between seven and 19 times finer than granular activated carbon, another filter that uses activated carbon. A binding agent holds the individual granules of carbon block together, keeping them locked rigidly in place. Whereas granular activated carbon is vulnerable to channels forming from flowing water, carbon block filters are not.

Where does the activated carbon come from? One source is bituminous coal, which is cheap but not as clean as other sources. Wood-based carbon is renewable, and can even target specific pollutants. However, it involves waiting for trees to grow, which can take many years to reach maturity. Coconut shells are proving to be an ideal answer to carbon sourcing. They have the highest levels of microporosity, as well as better purity and a higher environmental standard in manufacturing and sourcing.

How Do Carbon Block Filters Work?

A carbon block filter uses three distinct processes to filter water.

  1. Mechanical filtration: This part of the process involves water flowing through the carbon block itself. The porosity of the carbon block strains out impurities at a minimum of 0.5 microns in size. This process is similar to a sieve, in that the size of the pores determines the size of impurities that are filtered out.
  2. Physical adsorption: While the “sieve” process in step one strains out impurities, the activated carbon attracts contaminants by itself. The large surface area of activated carbon provides room for dissolved pollutants to accumulate. Meanwhile, the binders holding the carbon granules together are specially designed to keep the surface of the carbon clear. This keeps the surface from getting clogged with particulates, allowing it to adsorb continuously.
  3. Electrokinetic adsorption: Some carbon block filters are wrapped in an outer membrane that allows water to pass through it. As this happens, the wrap gains a net positive charge that attracts negative ions. These are common in specific pollutants, giving it an advantage in filtering water with these contaminants.

Each carbon block is a cartridge formed to specific dimensions, while end caps on the block direct water through its pores. In high-quality carbon blocks, the structure of pores is uniform across the block itself. This is important in mechanical filtration, as it means there is no path of least resistance. In other words, water will not favor any one path over another — the entire carbon block will filter equally. That maximizes the life of the carbon block.

How Affordable Is a Carbon Block Filter?

A carbon block filter is one of the more affordable water filtration types, largely due to the elegant design of the filtration system. Whereas other systems require high power consumption, chemical additives, or frequent filter replacement, carbon block filters do the majority of their work via a natural mechanical process. Additionally, carbon block filters are highly customizable, allowing you to save money in the design stage by fitting the filter system to your existing space.

Carbon block filters offer the best cost-to-value ratio of any water filtration system. No other system can remove impurities such as lead, volatile organic chemicals, particulates or microscopic cysts in such a short time.

Pros and Cons of a Carbon Block Filter

The advantages of the carbon block filter are as follows:

  • It is a green technology, particularly with the use of coconut or nutshell carbons.
  • It is excellent at removing small particles that can be a health concern.
  • Its small profile and form make it able to be produced in multiple designs, making it versatile in its applications.
  • It goes beyond odors and tastes to target more insidious health threats — highly effective at filtering a wide array of health-threatening contaminants.
  • High contact time within carbon material means more thorough filtration.
  • It does not drastically alter the pH, as can be the case with reverse osmosis.
  • They are dense enough that they do not promote bacteria growth due to matter buildup.
  • They can be custom-made with different-sized pores to target specific pollutants and bacteria.

The disadvantages of the carbon block filter are as follows:

  • Its high contact time — that is, the amount of time the water spends in the carbon block — makes it slower, meaning it is not generally recommended for very high flow-rate applications.
  • It may require regular cleaning to prevent the buildup of organic matter.

Method 2: Granular Activated Carbon

This type of filter still uses activated carbon to filter water, but it does so in a slightly different way. Whereas a carbon block is composed of finely ground carbon held together by a binding agent, granular activated carbon contains loose carbon granules that are not held together. Furthermore, the granules are larger than those in a carbon block. This results in a coarser mesh, which allows more contaminants through, but also allows a faster filtration time.

Granular Activated Carbon Filters

Granular activated carbon filters typically get used in municipal, commercial and industrial applications, and also at the point of entry into a home or business. Because they allow water to pass through quickly, they are more suited for quick, low-intensity filtration such as removing larger particulates, tastes, and odors. In fact, they are often called “taste-and-odor” filters. The taste and smell of chlorine is a common complaint in tap water, and granular activated carbon filters are effective at removing it from water entering a building.

These filters are also similar to carbon block filters in that the carbon comes from coal, wood, or nutshells. As with the carbon block filter, nutshells are turning into the most promising option.

How Do Granular Activated Carbon Filters Work?

In granular activated carbon filters, the incoming water gets directed through a collection of loose, activated carbon that is contained to remain where it is. The water filters through the carbon, which contains a high degree of porosity thanks to its increased surface area. This carbon’s surface area can adsorb contaminants in the incoming water, letting it make a high degree of contact so the carbon can remove particles and other contaminants. In this way, it is similar to carbon block filters.

The difference lies both in the loose distribution of granules and in the larger size of the granules themselves. The loose distribution allows the granules to shift, which can cause channeling to occur. This phenomenon refers to granules flowing as a result of the incoming water. That can eventually lead to paths of low resistance, through which more water will flow. The consequence is that this water will have very little contact with the carbon itself, and will, therefore, receive less filtration.

The larger size of the granules means, in turn, the size of the pores between them is much larger. Naturally, the sieve effect is less potent with granular activated carbon because of these larger pores. More particles can pass between the carbon granules, meaning less filtration and a higher risk of contaminants. That goes back to why the granular activated carbon filter is called a “taste-and-odor” filter — it is best for removing aesthetic pollutants like particulates, tastes and odors, but not necessarily for high-grade filtration.

How Affordable Is a Granular Activated Carbon Filter?

This type of filter is comparable in price to a carbon block filter. Best suited for applications where high flow rate and basic filtration are important, the filter does not allow the same degree of filtration as a carbon block filter for the price.

Pros and Cons of a Granular Activated Carbon Filter

The advantages of the granular activated carbon filter are as follows:

  • It is well-suited for points where water enters a home or building due to its high flow rate.
  • It is easy to install and remove.
  • It can remove aesthetic contaminants like chlorine from water, improving its taste and odor.

The disadvantages of the granular carbon filter are:

  • There is lower-quality filtration as a result of less contact time between water and carbon.
  • It needs frequent replacement to avoid buildup of organic material, which can breed bacteria — this is also a result of a lower density in the carbon.
  • A larger pore size results in more particulates getting through.

Method 3: Reverse Osmosis

Reverse osmosis makes use of a semipermeable membrane to strain pollutants out of water. This method has been in use for several decades. However, it cannot filter out soluble volatile organic chemicals and yet requires a large, complex and often cumbersome system. Reverse osmosis is still relatively thorough, with the ability to strain out 98 percent of incoming pollutants. The reasons many people do not choose it are its high cost, high energy requirements, its slow output and the amount of wastewater it produces.

Reverse Osmosis

How Does Reverse Osmosis Work?

Reverse osmosis starts with a pre-filter through which water passes. It can remove particulates and pollutants as small as five microns. After this pre-filter, the water enters a high-pressure chamber. This pressure chamber is lined with a semipermeable membrane, which strains 98 percent of remaining pollutants, including cysts and bacteria. It also happens to remove some minerals that are essential to health and taste.

By forcing water with a higher concentration of solute through the membrane and into a low-solute concentration, the membrane naturally accumulates waste that needs to be flushed. This generates wasted water, sometimes in ratios as high as ten to one, that flows to the drain and otherwise gets unused.

When the water passes through the semipermeable membrane, it goes through an adsorption filter that serves to improve aesthetic qualities like odor, color and taste. It sits ready for use in a pressurized container. This container can introduce its own flavor into the water, and so a final filter is necessary to remove any such undesirable taste.

How Affordable Is Reverse Osmosis?

Reverse osmosis is expensive. The cost is due to the size and engineering requirements of the unit itself, which includes several chambers, filters, membranes, and sometimes electrical power.

Pros and Cons of Reverse Osmosis

The advantages of reverse osmosis are as follows:

  • It does a thorough job in filtering water.
  • It can remove small particulates.

The disadvantages of reverse osmosis are as follows:

  • It can only produce one to twenty gallons per day.
  • It requires a large number of filters.
  • It is expensive.
  • Without a UV light, it cannot remove small microorganisms.
  • It is high in waste.
  • The membranes have a short lifespan.
  • Reverse osmosis systems are cumbersome.
  • Water flavor is flat.

Method 4: Distillation

Whereas carbon filtration relies largely on the natural pressure and flow of water to filter out impurities, Distillation relies on electricity and energy. Water gets boiled, leaving some impurities behind, with water vapor and other volatiles escaping. This water vapor is then condensed to form liquid water. A carbon filter may be necessary to remove volatile organic compounds or other contaminants that may boil along with the water. Afterward, the residue in the boiling chamber must be flushed out to prevent buildup.

Distillers come in either air-cooled or water-cooled units. Air-cooled units are generally more efficient in their water usage.

Due to the amount of energy input required to boil water continuously, each gallon has an operating cost of between $0.20 and $0.40 from energy alone. Each gallon requires roughly three kilowatt-hours. Another downside of this method is that it produces water that tastes flat, as it does not contain healthy minerals.

Pros and Cons of Distillation

The advantages of Distillation are as follows:

  • They produce clean water, free of inorganic compounds.

The disadvantages of Distillation are as follows:

  • They cannot remove volatile organic chemicals, which evaporate with the water vapor.
  • They are expensive.
  • They are time-consuming, with a lot of time required for each gallon of water.
  • They have higher operating costs due to electricity consumption.

Comparing the Four Methods

Carbon block filters tend to outperform other options regarding overall filtration, maintenance, cost and taste. Granular activated carbon filters are low-cost and can remove aesthetic contaminants such as undesirable odors, tastes, and colors. Unfortunately, they do not allow for much contact time between water and carbon, making them unable to remove many of the more hazardous contaminants. These filters are excellent choices for pre-filters for point-of-entry use, with carbon block filters used after to achieve better drinking quality.

Carbon block filters also compare well with reverse osmosis, which is hampered by slow filtration rates, expensive equipment, and inefficient use of water. Distillation is similarly hindered by inefficient energy consumption, slow filtration, and an inability to remove volatile organic chemicals.

Learn More About Carbon Block Filters at Multipure

Multipure Solid Carbon Block

Multipure has the unique ability to provide partners and clients with a complete, turnkey solution for water treatment and filtration. We leverage more than 40 years of manufacturing carbon block and hybrid drinking water treatment to provide the highest-performance solutions to our customers.

Multipure filters and purifiers are useful in the home, in the yard or in the field. Products include drinking water systems for the home, filters for use in the yard or garden, and military-grade emergency filters for the field. NSF certification guarantees high product performance.

Come explore our line of carbon block filters, and contact us with any questions.