1. The most obvious filtration process is known as mechanical filtration. Mechanical filtration works like a sieve, where particulates with a larger physical size than the pores of the filter are strained out. Carbon blocks can mechanically filter particles as small as one-half micron (submicron).
2. Another filtration process used in some carbon blocks with a specially designed outer wrap is known as electrokinetic adsorption. This process works as water passes through the outer wrap, which causes the material in the wrap to acquire a positive molecular charge that attracts negative ions of certain pollutants.
3. Carbon blocks also utilize physical adsorption. This is the process by which the carbon itself attracts pollutants. Activated carbon particles have a very large surface area to attract and hold pollutants. Specially formulated binders used in compressed carbon blocks can avoid masking the surface of the carbon, thereby optimizing its ability to reduce levels of pollutants.
NSF standards for drinking water filters have evolved beyond simply measuring the level of the contaminant before and after filtration. Testing standards also dictate the sample water characteristics, such as pH, temperature, and levels of commonly occurring minerals like calcium and magnesium. The standards dictate testing and sampling procedures as well. These standards assure that the filter will perform under “real world” water conditions.
The NSF/ANSI testing standards have been adopted by other
certification providers, including Underwriters Laboratory (UL) and
the Water Quality Association (WQA).
Carbon block filter systems are evaluated under NSF/ANSI Standards 42 and 53. Standard 42 is referenced for filters that remove aesthetic contaminants (e.g., chlorine, taste and odor), and Standard 53 is referenced for filters that reduce levels of contaminants of health concern (e.g., lead and arsenic).NSF is a non-profit testing lab which is recognized by the EPA to rest and certify water filters.