Essentially there are three types of water filters, or more accurately, three types of water filtering methods. They are mechanical, chemical oxidation reduction (redox), absorption. Following is a description of how each works and examples of filtering media for each process
This is simply having a barrier that has holes smaller than what it is that you want to filter out. This method of filtration removes tiny particles that are suspended in the water such as dirt, silt, sand, sediment, rust and other un-dissolved substances. As water passes through the the media the particles are trapped or blocked and effectively removed from your water.
Depending on the quality and/or type of the filtering media particulates as small as 0.3 microns can be stripped from your drinking water. For reference purposes, a micron is equal to 1/25,000 of an inch, the diameter of one strand of your hair is around 100 microns.
A variety of materials are used to produce mechanical filtering media. Ceramics and various resins comprise the majority of this type of water filtration.
Oxidation-Reduction Process or Redox
Oxidation/Reduction Technology is a process where by electrons from one atom or molecule are transferred to another. What this means is that when you mix two dissimilar metals you get an electrochemical process that oxidizes a host of chemicals found in our municipal water supplies. The heavy metals like aluminum, cadmium, lead and chromium are removed by the electrochemical process. These metals are attracted to the media, very similar to a magnet.
KDF Fluid Treatment, Inc., manufactures the most widely used media of this type, a coper and zinc alloy, and has held the patent since 1987.
Adsorption: Activated Carbon
Activated carbon absorbs organic substances that cause your water to smell and taste bad. It also has the ability to remove pesticides, chlorine and its byproducts. This product is very porous, so much so that the carbon in an average countertop filter would have a surface area of 200 football fields.
The term “activated” refers to a process that makes the carbon more porous than it is naturally. Activation is achieved using steam, a chemical process or by controlled production processes while creating the carbon
Activated carbon works like this: As water flows over the surface at sufficient pressure dissolved chemicals stick to the carbon allowing the water to continue. This process is called absorption.
Activated carbon can be grouped into three categories: carbon block (CB), granulated activated carbon (GAC) and powdered activated carbon (PAC). The CB variety works better at higher pressures, where the GAC is less expensive and works well with municipally supplied water. The PAC variety is less common.
The raw materials used for making activated carbon are usually coconut shell, wood, lignite, coal and the like. Coconut shell is considered to be the preferred material when making filters for drinking water due to its tendency to leave the water tasting better.
It is important to remember that water filters do not completely remove contaminates, they can only reduce them. However a good quality water filter will strip most of the unwanted contaminants it is designed to remove. Be sure to buy only water filters certified by the National Sanitation Foundation (NSF). These filtration systems will have been tested against their claims. In other words you will know what you are getting.