What type of filter relies on sand to purify pool water?

The type of filter that relies on sand to purify pool water is commonly referred to as a high-rate sand filter. These filters operate by using a bed of sand to trap dirt and debris as water flows through them. Water enters the filter and passes through the sand, where particles are captured and the cleaned water is returned to the pool.

When dealing with other types of filters mentioned, diatomaceous earth (DE) filtration uses a powdered substance made from the fossilized remains of tiny aquatic organisms to achieve a finer level of filtration. Fiber cartridge filters utilize a fabric-based medium to capture contaminants, which is different from the sand material.

Thus, when identifying the filter type that specifically utilizes sand for purifying pool water, "high-rate sand" is the correct designation for this filtration method, which effectively handles large volumes of water and is widely used in residential and commercial swimming pools.