Redox potential: for a water body, there are often a variety of redox pairs, forming a complex redox system, and its redox potential is the comprehensive result of redox reaction between a variety of oxidizing substances and reducing substances. Although this index can not be used as an index of the concentration of certain oxidizing and reducing substances, it can help us understand the electrochemical characteristics of water and analyze the properties of water. It is a comprehensive index. The redox potential of water must be measured on site. The determination method is to use platinum electrode as indicator electrode, saturated calomel electrode as reference electrode, and water sample as primary battery. The redox potential of platinum electrode relative to calomel electrode is measured by transistor millivoltmeter or universal pH meter, and then converted into redox potential relative to standard hydrogen electrode as report result. The formula is as follows: En=Eind+Eref Where: en -- redox potential (MV) of water sample; Eind -- measured redox potential (MV); Eref -- electrode potential (MV) of saturated calomel electrode at measured temperature, which can be found in physical chemistry manual or relevant data.