Polyaluminium chloride has good low-temperature coagulation water treatment effect and sedimentation function. Generally, when the low-temperature water is less than 5 °C, the coagulation and turbidity effect of the traditional coagulant such as aluminum sulfate and other water purifying agent products will be significantly reduced. The effluent water quality deteriorates, and in the use of polyaluminium chloride, whether it is low-temperature water or high-temperature water, good coagulation and turbidity effects can be obtained. Polyaluminium chloride not only has strong agglomeration and turbidity effect, but also has certain Decolorization, the effect of humus removal. Under the same treatment conditions, the use of polyaluminium chloride can obtain a lower residual turbidity than other aluminum salt water purifiers, so that the same water treatment results can be obtained at a lower dosage, and the range of use of polyaluminium chloride is also higher. The traditional aluminum salt water purifying agent should be widely used. The traditional aluminum salt water purifying agent generates aluminum hydroxide to form a precipitate at pH>8.0, which reduces the effect of water treatment, while the polyaluminium chloride has a pH value of <10. Both of them will get better water treatment effect. At low or medium pollutant concentration, the polymerization of aluminum chloride is much better than the traditional aluminum salt, especially in the case of large acidity or alkalinity. Aluminum can significantly improve the efficiency of solid-liquid separation, improve the function of sedimentation filtration and sludge dewatering, and thus shorten the residence time of the sedimentation tank. The residual aluminum content in the water after the treatment of polyaluminium chloride is very low. The residual aluminum content in the traditional aluminum sulfate treatment water is 150-255 mg/L, and the residual aluminum content in the treated aluminum chloride treatment water is only 40-55 mg/L, and Will affect the acidity and alkalinity of raw water.