Water temperature: many physical and chemical properties of water, such as density and viscosity, are closely related to water temperature. Meanwhile, solubility of dissolved gases (such as oxygen, carbon dioxide, etc.), aquatic organisms and microbial activities, chemical and biochemical reaction speed, salinity and pH value will also be affected by the change of water temperature. The temperature of water varies greatly depending on the water source. Generally speaking, the groundwater temperature is relatively stable, usually 8-12 ℃; The surface water changes greatly with seasons and climate, and the range of change is 0-30 ℃. The temperature of industrial wastewater varies greatly due to the industrial type and production process. The water temperature measurement shall be carried out on site. The commonly used measuring instruments include water temperature meter, reverse thermometer and thermistor thermometer. Note: the thermometer should be calibrated regularly. （1） Water temperature meter method (gb13195-91) Mercury thermometer is installed in a special metal sleeve, and the sleeve is provided with window hole for thermometer reading. A lifting ring is arranged at the upper end of the sleeve to fasten the rope. The bottom of the sleeve is tightly tightened with a water holding gold chip cylinder with only holes. The ball part of the water temperature gauge shall be located in the center of the metal cylinder. The measurement range is - 6 ~ + 40 ℃, and the index value is 0.2 ℃. This method is suitable for the determination of surface water temperature. （2） Reverse thermometer method The closed end (pressure proof) reverse thermometer (Fig. 3-12) is composed of the main temperature gauge and auxiliary thermometer assembled in the thick wall glass casing, and the two ends of the sleeve are completely closed. The main temperature meter is measured in the range of - 2 ~ + 32 ℃, the graduation value is 0.10 ℃, the measurement range of auxiliary thermometer is - 20 ~ + 50 ℃, and the index value is 0.5 ℃. The mercury column of main thermometer shall be flexible in fracture, the position of breakpoint shall be fixed, the temperature shall be corrected and the silver in the water shall be returned completely. The main and auxiliary temperature meters shall be fixed firmly. The reverse thermometer shall be installed on the reverse water collector. It is suitable for measuring water temperature of each layer with water depth of more than 40m.