1) Mechanical Filters
Mechanical filters are designed to provide a physical barrier against contaminants such as sediment, dirt, and other suspended particles.
There are many types of mechanical filters, including ceramic filters (which remove contaminants of all sizes, including pathogens, through a network of pores) and mesh filters (designed to capture suspended particles, such as sand and rust, while allowing water particles to pass through).
2) Adsorption Filters
An adsorption filter is a water filter that grabs contaminants and holds them in its pores (sort of like a sponge), a process called adsorption. Activated carbon filters are the most common type of adsorption filter. Activated alumina filters also reduce contaminants through adsorption.
There are several types of adsorption filters. Granular activated carbon (GAC) and carbon block filters are the two most common filters that provide carbon filtration. Carbon block filters are generally more expensive due to their design-the media is packed into a solid block, which allows for more thorough removal of contaminants.
3) Ion Exchange Filters
Ion exchange is a process that exchanges ions on a charged resin.
The most common use of ion exchange in water treatment is in water softeners, which exchange magnesium and calcium ions for ions that do not affect water hardness, such as potassium or sodium. This prevents scale from forming and helps reduce existing scale in plumbing fixtures and pipes.
Some water filters, such as kettle filters, combine ion exchange resins (usually hydrogen-based) with other water filtration media, such as carbon media, to remove substances such as fluoride, arsenic, nitrates, and sulfates.
Any substance with an electrical charge can be effectively removed with an ion exchange filter.
4) Membrane Filters
Membrane filters use a process called membrane separation to remove most of the total dissolved solids from a drinking water supply. They force water through a semi-permeable membrane under pressure. The membrane pores are so small that only water (and dissolved salts and solids in the case of ultrafiltration) can pass through. The removed contaminants are flushed down the drain along with a small amount of wastewater.
5) Deionizing Filters
A deionizing filter, also called a "water polishing" filter, is a device that exchanges positive hydrogen and negative hydroxyl molecules with contaminants (positive and negative) in the water, a process called ion exchange.
Deionized water has almost all of the positive and negative ions removed, including anions such as sulfate and chloride, and cations such as copper, calcium, sodium, and iron.
