Sand filters are used as a step in the water treatment process of water purification.

There are three main types; rapid (gravity) sand filters, upward flow sand filters, and slow sand filters. All three methods are used extensively in the water industry throughout the world. The first two require the use of flocculant chemicals to work effectively while slow sand filters can produce very high-quality water with pathogens removal from 90% to >99% (depending on the strains), taste, and odor without the need for chemical aids. Sand filters can, apart from being used in water treatment plants, be used for water purification in singular households as they use materials that are available for most people.

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The main benefit of a sand filter is the simple system which, in many cases, can be used to obtain considerable yields. A sand filter can be placed in various phases of water management – as a pre-treatment, as side-stream filtration and as a polishing filter. A sand filter often provides an effluent with potential for re-use.

However, chemicals sometimes need to be added to improve the yield of the sand filter. A disadvantage of sand filtration is the rinse water that is created when the sand filter is cleaned. This heavily polluted water must be treated and disposed of. To limit the load on the filter, a preliminary sedimentation step is implemented for heavily loaded wastewaters (a lot of suspended and sinkable matter). This helps to avoid repetitive re-rinsing of the filter.

Discontinuous sand filters are often placed in parallel set-up in order to keep the process running when one of the filters is being cleaned.