What is the use of sand in water?

A sand filter, or sand water filter, makes use of sand to filter water. The water to be purified slowly sinks through the sand of the sand filter, leaving the dirt particles from the water behind in the fine pores of the sand.

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Keeping this in consideration, what happens if we run out of sand?

What is sand made of? Sand is typically made mostly of varying amounts of material weathered from inland rocks (or seacliff material) and transported to the beach on the wind or in rivers, and/or shells and other hard parts precipitated out of the ocean water by marine organisms. Sand therefore records processes at a variety of timescales.