Reverse Osmosis Versus Solid Carbon Block Filters

Reverse Osmosis Versus Solid Carbon Block Filters

Posted by Kenton Jones on May 13th 2020

Continuing our May 2020 Spotlight: “Comparing Water Treatment Technologies,” for this article we will be discussing Reverse Osmosis (RO) water treatment in comparison to Solid Carbon Block water treatment.

Reverse Osmosis

Reverse osmosis reduces contaminants in drinking water by pushing the water through a semipermeable membrane, allowing water to pass through while contaminants such as heavy metals, salts, and inorganic compounds remain behind. This method has been in use for several decades, due to its ability to strain out about 98 percent of waterborne contaminants. It is not without drawbacks, as it cannot filter out soluble volatile organic chemicals (VOCs), and by its nature it is large, complex, and cumbersome. RO systems are generally high cost, with high energy requirements, high water waste, and a slow filtered water output.

How does an RO system work?

A typical RO system starts with one or more sediment pre-filters, which trap larger particulate matter in the water. The water then proceeds through a solid carbon block pre-filter to trap organic chemicals and chlorine before the water reaches the RO membrane. At the RO membrane, the high-pressure chamber forces the water through the membrane to remove cysts, some bacteria, and some minerals. After the RO membrane, the water is sometimes treated by an optional solid carbon block post-filter to trap any remaining contaminants, as well as an optional ultraviolet (UV) light to sterilize any remaining microbes in the water. The fully-treated water is then stored in a filtered water reservoir for use.

The RO membrane accumulates contaminant waste that must be flushed into wastewater; the ratio of water that must be flushed as waste can vary, but can occur in ratios as high as ten to one of wastewater to filtered water.



Solid Carbon Block

Carbon block filters are highly effective at removing contaminants, odors, and tastes from water via the use of activated carbon. This type of carbon is highly porous, making it able to adsorb more contaminants due to its large surface area.

The key distinguishing feature of carbon block filters is the size mesh that the carbon creates. Carbon blocks are made up of particles that are between 0.045 mm and 0.18 mm, making them between seven and 19 times finer than granular activated carbon (GAC). Because the individual granules of the carbon block are locked in place through compression and a binding agent, carbon blocks are not susceptible to channels forming from flowing water (a common occurrence with GAC filters).

Carbon blocks are versatile in their usage, as their size can be customized during the manufacturing process. Because of this, they are used in a variety of filtration appliances, from small faucet-mount filters, to refrigerator filters, to moderate-sized below-sink drinking water systems, to large whole-house water filtration systems and more. This versatility means that carbon block filters can vary in size, capability, and cost.

How does a solid carbon block filter work?

A carbon block filter uses three processes to filter water.

  1. Mechanical filtration: This process occurs when water flows through the carbon block itself. The tiny pores of the carbon block strain 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: As the filter mechanically strains out impurities, the activated carbon attracts contaminants to itself. The large surface area of the carbon block provides room for dissolved pollutants to accumulate. Meanwhile, the binders holding the carbon granules together keep the surface of the carbon clear, preventing the surface from getting clogged with particulates, and 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.

Higher-quality carbon blocks – such as ones manufactured by Multipure – possess a pore structure that is as uniform across the block as possible; 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 and performance of the carbon block.

Because carbon block filters perform the majority of their filtration work via natural mechanical processes, they require no power or chemical additives. Additionally, carbon block filters are highly customizable, giving them the versatility to use in products and systems of varying shapes and sizes.


At first glance, the primary differences between Reverse Osmosis and Solid Carbon Block water treatment systems come down to size, price, and complexity. RO systems are generally larger, more expensive, and more complex than solid carbon block systems. While individual solid carbon block systems will vary in size, capability, and price, virtually all RO systems are bulky and complex enough to require professional below-sink installation.

RO systems may feel more “complete” than carbon block systems, in that they utilize carbon block pre-filter and post-filter elements in addition to an RO membrane, but more is not always better. RO systems are much slower, more limited in available water supply due to needing a clean water reservoir, and much more expensive and difficult to maintain due to their many filter elements. The RO reservoir tank also needs to be replaced typically after 5-10 years. In addition, the removal of beneficial minerals in the water results in both a “flatter,” less appealing taste, and water that is more acidic than regular tap water.

Solid carbon block systems may feel “simpler” at a glance, but that simplicity is an advantage when it comes to water filtration. They are easier and cheaper to install and maintain, offer real-time water filtration, and preserve the beneficial minerals in the water. This results in cleaner, healthier, better tasting water.

And when it comes to solid carbon block performance, not all carbon blocks are the same; Multipure’s carbon block systems are NSF-certified to treat the broadest array of contaminants in drinking water – a claim that not all carbon blocks can approach. Multipure’s Aqualuxe is an industry leader when it comes to drinking water treatment performance, NSF-certified to protect the taste and odor of your water ( NSF Std. 42) and the healthfulness of your water (NSF Std. 53) against harmful contaminants like VOCs, DBPs, arsenic, lead, and PFOAs. It is further NSF-certified to protect your water against pharmaceuticals and other emerging contaminants (NSF Std. 401), as well as serve as a microbiological purifier (NSF Std. P231) to protect your water against bacteria, viruses, and live cysts.

In a market saturated by thousands of water filters, this is why Multipure is so confident in the power, performance, and protection offered by our solid carbon block drinking water systems. Taste the Difference of Multipure.