Guide to the Different Methods of Water Filtration
Posted by Kenton Jones on Apr 9th 2021
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.
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 They Work?
A carbon block filter uses three distinct processes to filter water.
- 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.
- 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.
- 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.
The nature of a densely compacted carbon block means that the water that passes through it makes contact with a large surface area of activated carbon, and for a relatively long amount of time. Because of this, the carbon block is ideally suited for physiochemical adsorption to take place. Within the water stream, the contaminant particles experience an attractive force with the activated carbon that comprises the carbon block, either through Van der Waals forces or as a result of chemical bonds. Because of this, the remaining contaminant particles that have not been electrokinetically adsorbed by the prefilter or mechanically trapped by the carbon block pores are finally adsorbed to the surface of the filter media itself. This includes contaminants such as pesticides, herbicides, and certain heavy metals.
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 Carbon Block Filters
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 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.
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.
Method 5: UV Water Purification
Ultraviolet (UV) water purification allows households to treat their water with UV light. At a high enough intensity, UV light produces enough radiation to deactivate a microorganism's DNA.
Typical UV water purification systems are placed at the front of a flow chamber, where water passes through before it reaches the consumer. As the water goes through the flow chamber, the UV light renders bacteria and other microbes sterile.
These purification systems are commonly used for their ability to treat bacteria, viruses, protozoa, and parasites. A few of these include Cryptosporidium, Giardia, E. coli, Hepatitis A, and Rotavirus. As such, one of the major benefits of using UV water purifying systems is its ability to deactivate microorganisms that could be living in your drinking water. Additionally, the process doesn't alter the water's taste because it doesn't use any chemicals to purify the liquid.
Some of the downsides to UV water treatments include:
- Only treats microbes: UV light can only remove microorganisms, meaning it can't treat chemicals and other contaminants. Some of these contaminants include salts, heavy metals, lead, perfluorooctanoic acid (PFOA), and chlorine. This lack of filtration can be a problem if your water contains a lot of them. To remove these substances, you'll have to invest in a prefilter or filtration system to pair with the UV purifier.
- Requires electricity: For homeowners who want to avoid a higher electric bill, the UV system's need for electricity will be a barrier to this technology. Besides higher energy costs, the need for power also makes this option an inconvenient choice if you want something that will work in a survival situation or emergency.
- Needs clear water: Since UV light treats microorganisms, it's only effective with clear water. Particle-filled water will block the UV light from reaching the microbes. Private well water can often be murky and will need a prefilter for a UV filter to work.
Method 6: Ionizers
Ionizers raise the pH of regular water through electrolysis. In this ionization process, water passes over electrically charged plates. As it travels across the plates, the water is separated into acidic and alkaline streams. This separation gives consumers softer, low-acidity water. An ionizer's primary selling point as a water treatment system is its ability to produce alkaline water, defined by its pH level of seven or higher.
Though there are a lot of unsubstantiated claims about how healthy alkaline water is, it does come with some proven benefits that can make an ionizer attractive to buyers. For example, alkaline water's negative oxidation-reduction potential (ORP) level turns the liquid into an antioxidant, with studies also finding that drinking alkaline water can facilitate better hydration levels. Scientists have even found evidence that alkaline water can alleviate some of the symptoms of acid reflux.
However, a major disadvantage of ionizers is that they aren't equipped with a prefilter capable of reducing contaminants — they only raise the pH of the water. This problem leaves consumers with water that might contain contaminants like hormones, lead, pesticides, viruses, bacteria, asbestos, and pharmaceuticals. Additionally, alkaline water usually doesn't have as many beneficial minerals as other types of water as these are removed in the water treatment process.
Comparing the 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.
Which Water Filtration System Is Best for My Home?
Now that you have a better idea of what each type can offer you, you're ready to choose a filtration system for your home. Check out some of the top drinking water systems from Multipure below:
- Aqualuxe: With a powerful PureBlock carbon block filter backing it up, the Aqualuxe is for buyers who want a high-tech water purifier that can significantly reduce bacteria and viruses, contaminants such as asbestos and arsenic, and a wide range of chemicals. Besides its water-purifying capabilities, the Aqualuxe comes with next-gen Wi-Fi monitoring, a leak detector, QuickSecure plumbing attachments, and FilterSync technology. The filter is perfect for most homes, as you can install it under the sink or on the countertop.
- Aquaperform: The Aquaperform Drinking Water System utilizes solid carbon block filter technology to treat contaminants in your drinking water. Like the Aqualuxe, it even comes with arsenic-adsorptive media, which makes it a popular choice for buyers wanting to avoid ingesting the deadly Arsenic V and other contaminants like asbestos, mercury, and lead. This system comes in stainless-steel housing that you can attach under your sink or straight onto your faucet.
- Aquaversa: Like the Aqualuxe and Aquaperform, the Aquaversa uses solid carbon block filter technology that meets NSF standards for contaminant reduction. This system is one of the best mid-range water filtration options on the market. You can place it below the sink or on your kitchen sink faucet. One major selling point for homeowners is its generous 750-gallon-capacity filter.
- Aquamini: As the smallest water filter on this list, the Aquamini works well as a travel drinking filter that uses a solid carbon block filter to give users clean water. Its compact design and 250-gallon-capacity filter make it perfect for single families, college dorm rooms, and those who want to take a water filtration device with them on business trips or family vacations. You can use the Aquamini on the countertop or below the sink. Since it's smaller and has a lower capacity compared to others on the list, it is one of the most affordable water filters available today.
Why NSF Certification Should Influence Your Home Filter Purchase
Make sure your home water filter has NSF certification. A system with certifications means the product has gone through third-party water filtration tests that show it meets multiple benchmarks. For example, NSF certification proves the system meets the manufacturer's claims about contaminant reduction, has a structurally sound design, and avoids adding anything harmful to the water. It also ensures that manufacturing processes stay consistent and marketing materials remain accurate and truthful.
It's also important to note that not all NSF certifications are the same. There are a number of NSF certifications that deal with different factors. For example, NSF Standard P231 deals with the ability to purify bacteria, live cysts, and viruses, while NSF/ANSI Standard 42 only refers to aesthetic effects. Some companies will receive a single NSF certification for a product and display the seal on their marketing materials, implying that their product filters more than it actually does.
For example, a company could have an NSF certification for only purifying aesthetic effects and still display the NSF seal. As you search for a water filter, ensure that the company you're buying from has received multiple NSF certifications for their product, especially if you're looking for a specific kind of filtration type.
Multiple NSF certifications mean you can have confidence in your drinking water and give your family, pets, and visitors high-quality, clean water. Only choose a water filtration system if it has the relevant NSF certifications that pertain to your needs. Some companies will claim their products have been tested according to NSF standards or similar regulations but will not have the proof an actual certification provides.
Learn More About Carbon Block Filters at Multipure
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.