Comparing Carbon Block, Reverse Osmosis and Other Common Water Filtration Methods

Comparison Chart

The general public is justifiably confused about differences among water filtration approaches and their relative efficacy. When one begins shopping for a water filtration device, he is immediately presented with a rather bewildering set of choices and the daunting task of choosing from among reverse osmosis, KDF, carbon block and even distillation – to name the most common. In the following article, we have endeavored to describe each of these approaches in limited detail and then compare and contrast these various types of filtration technologies to assist you in making an informed decision when it comes time to purchase a water filter system.

Carbon Block Technology

With carbon block filters, water is forced through the pores of the densely compacted carbon block, where a combination of mechanical filtration, electrokinetic adsorption, and physical/ chemical adsorption take place to reduce a wide range of contaminants. Solid Carbon Block technology can reduce chlorine, taste and odor problems, particulate matter, and a wide range of contaminants of health concern -- cysts (cryptosporidium and giardia), VOCs (pesticides, herbicides, and chemicals), certain endocrine disrupters, Trihalomethanes (cancer-causing disinfection by-products), heavy metals (lead, mercury), turbidity, MTBE, Chloramines and asbestos. Solid carbon block filters do not remove healthful, naturally-occurring minerals, require no electricity, and do not add salt or silver to the water

Reverse Osmosis

Reverse osmosis (RO) has been known for more than a century, but it did not become a commercial process until the early sixties when a special membrane was developed (1,2,3,4). Because RO operates at a comparatively low temperature and is relatively energy efficient, it is employed in various applications, e.g., desalination, treatment of waste water, reclamation of minerals, concentration of whey and other food products, and purification of water. While RO will remove certain contaminants and additives that carbon block filters will not (i.e fluoride and nitrates for example), it has a number of downsides as well. These include: RO has no independent ability to reduce most Volatile Organic Chemicals (VOC's); it has very low output - takes up to 24 hours to process 5 gallons of water; you must have a holding tank to store the processed water; considerable water is wasted - for every gallon processed, 3 to 9 gallons are wasted and it removes minerals and trace elements essential to good health.

In the RO process, feed water is passed through a prefilter after pH adjustment, and is pumped to the membrane modules at the designed pressure. The product water is then pumped to a storage tank and the concentrate is drained (6). Most RO units with a cellulose acetate membrane are designed to operate between 55 F - 86 F. (13 C - 30 C). In practice, the feed water may go through any one or a combination of several of the following pretreatments: sand bed, chlorinator and retention tank, anthracite filter, activated charcoal filter, degasifier, microfilter, neutralizer, and deionizer, depending on the condition of the feed water and the desired quality of the product water. Since water conditions may vary from time to time, adequate pretreatment must be provided so that the dissolved solids and the bacterial level of the feed water, after prefiltration, can be controlled within the designed limits. In othere words, to get adequate treatment and a resulting safe water product, RO must be combined with othere technologies such as carbon block and/or granulated activated carbon.

Charcoal Filters or Granulated Activated Carbon (GAC)

These come in powdered or granulated form which allows water to flow around rather than through the carbon.Referred to as taste and odor filters because of the limited contact time the water has with the carbon.

KDF

In the KDF application, water passes through a bed of a media made of a special high-purity alloy blend of two dissimilar metals - copper and zinc KDF-55D. This media, patented in 1987 by KDF Fluid Treatment, Inc., is a major advancement in water treatment technology that works on the electro-chemical and spontaneous-oxidation-reduction (redox) principles. Chlorine is instantaneously and almost inexhaustibly oxidized.

Silver-Charcoal Filters

Same as Charcoal Filters above; however, uses silver to inhibit the growth of bacteria while water sits in filter.
Silver ingested in certain doses can be poisonous to the human body; therefore, it must be registered with the EPA as containing a poisonous substance.

Limited Media Filters

As the demand for quality drinking water continues to grow, new types of media will be test-marketed, from metal shavings to coconut shells. Some materials can be quite ”exceptional” in reducing a particular contaminant in the water, but there is a wide range of contaminants that should be addressed - not one or two.