Of the three filtering options available to the residential pool owner, Sand, Cartridge and D.E., sand is probably the most popular of the these. The main reasons for this, they are simple, effective, usually cost less than the other options and require very little maintenance.

Without going into a bunch a technical jargon, this is basically how sand filtration works. The filter canister is filled with sand.  Not just any sand but a special sand (also known as pool grade #20 silica sand) because of the sharp edges between the granuales. Water enters the top of the filter canister and flows to the bottom through all of the sand. On its way to the bottom of the filter, debris in the water is being trapped within the sand granuales. At the bottom of the filter there is usually some kind of underdrain with slots in it to hold the sand while the clean water passes thru. Over time, the sand in the filter becomes dirty and requires cleaning. This is done by turning a valve on the filter canister and reversing the direction of the water. This is commonly referred to as backwashing the filter.  The debris in the sand is washed out through the waste line. Sand filters typically filter out particles as small as 20 microns in size.