There are many definitions of a filter. A filter can be used in the context of air filtering, like in your home HVAC system. It also has many computer and engineering definitions such as in a search engine. You can choose to search for a particular topic, which only gets you the results for THAT topic and nothing else.

In this particular website, we’re interested in a water filter.  Dictionary.com defines a water filter as:

any substance, as cloth, paper, porous porcelain, or a layer of charcoal or sand, through which liquid or gas is passed to remove suspended impurities or to recover solids.

That’s a good definition. A water filter is made to reduce or remove anything in the water that is considered ‘undesirable’. There are many different types of filters that accomplish filtration by different designs. Each design has it’s own strengths and weakness’s based on the technology.  Often different types of filters are used in conjunction with each other to achieve the desired results. The various filter functions in general, can be defined as follows:

Tortuous Path Filters:

These filters generally utilize a media such as sand or ceramics.  When many small particles come together, they create a tortuous path that creates cavities in between the media.  As water makes its way through the media, it leaves behind particles that are bigger than the cavity sizes that the media makes. This filter removes undissolved solids only, unless the media is also able to adsorb or absorb certain contaminants.

Particle Size Filters:

These filters are composed of a material or materials like paper, cotton, glass fibers or a membrane.  The filter will allow only water and anything smaller than its rated pore size.  How much and what these filters will remove depends on the efficiency of the filter and the rated pore size.  A filter rated at 5 microns with a 50% efficiency will remove about 50% of all particles 5 microns in size. As the particles get larger, the efficiency improves.  Lower efficiency filters have what is known as ‘nominal’ ratings and high efficiency filters have ‘absolute’ ratings.

Adsorption Filters:

Adsorption filters are generally composed of a media of a fine grain to improve surface area contact.  Adsorption filters attract certain elements in water to attach themselves to the surface of the media and build up there.

Absorption Filters:

Absorption filters are usually a media type filter. These filters suck up certain parameters into the water similar to how a sponge sucks up water.  Different types of absorption filter can absorb different types of impurities in the water.

Ion Exchange Filters:

These are generally a fine media to increase surface area. These filters ‘take’ a parameter and ‘give’ something in place of that parameter. This is how water softeners work, taking calcium and magnesium ions in exchange for sodium ions.

Now that you are generally familiar with how filtration works, the following posts will apply these definitions into filters available for your water today.

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