The suspended matter in water is particles with a diameter of more than 1 ~ 4mm, which are mainly composed of sand, clay, protozoa, algae, bacteria, viruses and high molecular organic matter. Turbidity of water is also caused by such substances. These particles are very unstable and can be removed by precipitation and filtration. Suspended matter is the main source of turbidity, chroma and odor. Its content in water is also unstable and often varies with seasons and regions.