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Water pretreatment is a preliminary treatment carried out before water purification, in order to achieve good results during the purification process and improve water quality. Water in nature generally contains certain amounts of impurities, such as sediment, clay, organic matter, inorganic salts, microorganisms, and mechanical contaminants. The presence of these impurities significantly affects the efficiency of water purification; therefore, it is necessary to reduce or remove some of these impurities (mainly suspended solids and colloidal substances) before the actual purification process. This requires pretreatment, also known as pre-processing. There are many pre-treatment methods, mainly including pre-sedimentation, coagulation, clarification, air flotation, filtration, softening, disinfection, etc. After pretreatment, impurities in water such as suspended solids (turbidity), color, colloids, organic matter, iron, manganese, temporary hardness, microorganisms, volatile substances, and dissolved gases can be removed or reduced to a certain level. Pre-sedimentation refers to the natural sedimentation process that takes place at low flow rates or in a stationary state, such as in grit chambers and pre-sedimentation tanks. Coagulation is the process in which coagulants such as iron salts, aluminum salts, and polymers are used to form large particle precipitates (floc) with colloidal impurities in water through flocculation and bridging actions. Clarification is achieved by separating the large particle precipitates formed through the action of coagulants in a clarifier, thereby obtaining clear water. Filtering is the process of passing water through devices equipped with special filtering materials such as filter media, filter elements, or filter membranes, in order to retain or absorb impurities in the water. Softening involves using chemical agents such as lime water and baking soda to remove bicarbonate hardness from water ； Alternatively, methods such as ion exchange can be used to remove ions like calcium, magnesium, and iron from water; this process is known as softening. Disinfection involves using biocides (such as liquid chlorine, bleaching powder, ozone, ultraviolet light, etc.) to kill microorganisms in water and destroy organic matter.