Generally speaking, the salt content of the water (also called salinity) is the amount of salt in the water. Because of salt in the water generally exist in the form of ion, so salt content can also be expressed as the amount of the amount of cation and anion of the water and the amount of anion. When the water is relatively clean, the contents of organic substances in water are relatively few, and sometimes it is also used to approximate the salt content of water in the water.. When the water is particularly clean, the content of suspended solids is also less (e.g., groundwater), so it can sometimes be used to represent the salt content of water in the amount of total solids.. Natural water generally contains soluble substances and suspended substances (including suspended substances, particulate matter, aquatic life, etc.). Soluble substances in the main ion: potassium ion (K +) and sodium ions (Na +), calcium (Ca 2 +) and magnesium (Mg 2 +) and bicarbonate ions (HCO3 -), nitrate ion (NO3 -), chloride (Cl -) and sulfate ions (SO42 -) for the eight major ions in natural water is common, accounting for 95% ~ 99% of the total amount of ions in natural water. The classification of these main ions in natural water is often used as the main chemical index of the water body..