[[Image:granular high density carbonfiltration icon.jpg|thumbpng|right|350px|Granular80px]] The filter sand, consisting of 99.5% SiO2, high-density carbonis extremely low in trace metals and polycyclic aromatic hydrocarbons. This makes our filter sand the best sand available for monitoring well systems.]
In water treatment, granular filtration is a process where water flows through granular material (often sand) while suspended solids (sand, clay, iron and aluminum flocs) are retained, substances are biochemically decomposed and pathogenic microorganisms (bacteria, viruses, protozoa) are removed.
====Granular media, rapid rate filters and filter media====[[Image:granular high density carbon.jpg|thumb|right|200px|Granular, high-density carbon.]][[Image:filter sand.jpg|thumb|right|200px|Filter sand, supplied in bags and pallet packages. It consists of 99.5% SiO2 and is extremely low in trace metals and polycyclic aromatic hydrocarbons. This makes our filter sand the best sand available for monitoring well systems. Photo: [https://en.eijkelkamp.com/ Eijkelkamp Agrisearch Equipment BV.]]]
{|border="1" cellpadding="5"
|-
|-
|Granular media, rapid rate depth filter
|'''Sand, gravel, diatomaceous earth, coal, other minerals'''
|High
|Easy to Moderate
|-
|Slow sand filter
|'''Sand '''
|High
|Easy to moderate (community use)
|-
|Vegetable and animal derived depth filters
|'''Coal, sponge, charcoal, cotton, etc. '''
|Medium to high
|Moderate to Difficult
|-
|Fabric, paper, membrane, canvas, etc. filter
|'''Cloth, other woven fabric, synthetic polymers, wick siphons '''
|Varies: some low; others high
|Easy to moderate
|-
|Ceramic and other porous cast filters
|'''Clay, other minerals '''
|Varies: high- low, with materials availability and fabrication skill
|Moderate. Must be physically cleaned on a regular basis to prevent clogging and biofilm growth
|-
|Septum and body feed filters
|'''Diatomaceous earth, other fine media '''
|Varies
|Moderate to difficult; dry media a respiratory hazard
|Varies
|}
:: * Moderate typically means 90-99% reductions of larger pathogens (helminth ova and larger protozoans) and solids-associated pathogens, <br>but low(<90%) reductions of viruses and free bacteria, assuming no pre-treatment. With pre-treatment (typically coagulation),<br> pathogen reductions are typically >99% (high).<br> **High pathogen reduction means >99%.
===Acknowledgements===
* [http://www.who.int/water_sanitation_health/dwq/wsh0207/en/index5.html Managing water in the home: accelerated health gains from improved water supply]. WHO.
