The purpose of a Sand Filter is to purify water. A Sand Filter is made of layers of sand organized with coarseness of texture increasing downward allowing the sand to trap impurities in the water. The first documented implementation of a sand filter used for the purpose of water purification dates back to 1804 in Paisley, Scotland. There are three main styles of sand filters; a rapid or gravity sand filter , an upflow sand filter , and a slow sand filter. All three sand filter types are used extensively in water purification throughout the world. The first two sand filter methods , gravity and upflow, need chemicals to work effectively while the slow sand filter method can produce a very high quality water free from pathogens, odor and taste without the need for any chemicals. The most common consumer use of a sand filter can be found in most backyard swimming pools. The Sand filter is known to have the lowest maintenance requirements of the three types of swimming pool filters. You might only need to open up the tank of a swimming pool sand filter every 6 years or so. Whereas DE pool filters require annual maintenance where you have to remove and clean the internal grid assembly, and the third type of swimming pool filters , cartridge pool filters, do not backwash. It is necessary to remove the cartridge and clean the cartridge every so often, depending on the cartridge filter size. Sand filters are the easiest to type of swimming pool filter to operate and maintain.