A pre-filter is a filter that is installed before the main filter(s) in a water purification system. Its primary function is to remove larger particles and sediments such as sand, rust, and debris from the water. These particles can cause damage to the main filter(s) or reduce their effectiveness over time.

Pre-filters can be made from a variety of materials such as pleated polyester, spun polypropylene, ceramic, or mesh screens. They come in different sizes and micron ratings depending on the type of system and the quality of the water being treated.