Fiber filters contain spun cellulose, rayon, polypropylene, or cotton and are designed to take out sediment. The tightly wrapped fibers form a cylinder around a tube and pressure forces water through. They come in various densities from fine to course with the lower micron rating being the finer. The finer filters have a larger pressure drop with more particles trapped and will need more frequent changing..
The size of particles retained depends on the pore size, or the space between media fibers or granules. Most filters list an average pore size and are rated by the manufacturer according to the smallest particle they will remove. For example, a 10 micron filter would trap contaminants 10 microns or larger. The filter rating should be checked before purchase since many filters are only rated for particles 20 microns in diameter or larger. Filters with this rating may not effectively remove some silt particles, which generally range from 2.0-50 microns.
Three Typical Types of Cartridge Filters
String wound filters are primarily used for sediment and are made by winding polypropylene, cotton or rayon string around a tube. String wound filters have filtration efficiencies ranging from 50 to 60%. Their main disadvantage is a tendency to *channel flow under load and have poor dirt holding capacity. High differential pressures may cause string wound filters to release their accumulated particles.
Spun bonded polypropylene filters form a gradient density from outer to inner surfaces that traps particles throughout the thickness of its body and will not channel under pressure. The graded density structure traps larger particles on outer layers and smaller particles in the inner layer.
It is important to note that synthetic filters (made out of plastic fibers or resins) are a possible source of chemical contamination in themselves. These filters have better dirt holding capacity over string filters and the pricing is comparable.
Pleated filters are made of polypropylene, glass micro fibers and alumina nanofibers. The media is pleated to increase the surface area. They offer high retention in the 95% range and have excellent contaminant loading and holding capacities. The pleated filters higher surface area adds more holding capacity at lower differential pressures. These filters are available with filtration efficiency for micron size particles at better then 99.995%. Of the proper quality, the pleated filter is the best of the three types noted above.
Ceramic Filters
At the core of the ceramic filter element is Diatomaceous Earth (DE). DE contains fossil-like skeletons of microscopic water plants called diatoms, which are a type of algae. These diatoms range in size 
from less than 5 micrometers to more than 100 micrometers, and have a unique capability of extracting silica from water to produce their skeletal structure. When diatoms die, their skeletons form a diatomite deposit. In its natural state, diatomite is 85 percent inert silica. This type of filter is best suited to treat water that has low amount particulate sediment. DE filtration has shown superior capability for the removal of pathogens and asbestos. Odorless, tasteless, and chemically inert, DE is ideal for filtering water for human consumption.
The Importance of Certification from National Sanitation Foundation
(NFC)
In the last decade, interest in home water treatment products has grown tremendously. Unfortunately, it is not always easy for consumers to know whether or not a particular product will actually be as safe and effective as the manufacturer claims at reducing various contaminants from your water supply.
Filter industry regulation?
Federal, state or local laws do not regulate filtration products. The National Sanitation Foundation (NSF) a not-for-profit, non-governmental organization and the Water Quality Association (WQA) evaluate performance, construction, advertising and operation manual information. The NSF program establishes performance standards that must be met for endorsement and certification. The WQA uses the same NSF standards and equivalents to the American National Standards Institute (ANSI) accredited product certifications. Though these certifications and validations should not be the only criteria for choosing a sediment filtration system, they are helpful to ensure effectiveness of the system.
Since most filter cartridges look the same it is important to realize that particle holding efficiency of a filter varies according to the grade and density of the media. For example, a lower cost filter has 60% retention while its higher quality counter-part features an 80% rate of retention. When choosing a filter, base your selection on the retention efficiency that meets your needs. Price should not be your main point for purchase.
