Diatomaceous Earth (DE) filtration is a process that uses diatoms or diatomaceous earth—the skeletal remains of small, single-celled organisms—as the filter media. DE filtration relies upon a layer of diatomaceous earth placed on a filter element or septum and is frequently referred to as pre-coat filtration. DE filters are simple to operate and are effective in removing cysts, algae, and asbestos from water. DE has been employed in many food and beverage applications for more than 70 years and was used specifically to filter potable water during WWII. Since then, it has been used to produce high-quality, low-cost drinking water. DE filtration is currently one of the U.S. Environmental Protection Agency’s (EPA) approved technologies for meeting the require- ments of the Surface Water Treatment Rule (SWTR) and is most suitable for small communities that need to comply with the rule.