Water hardness is one of the indicators of water quality parameters, which can reflect the sum of the concentration of all metal ions dissolved in water except sodium and potassium ions. Hard water is water that contains high concentrations of minerals, especially calcium and magnesium. So what is water hardness? And how should the water hardness be tested? In this chapter, manufacturers of water quality online monitors come to understand related issues with you. What is water hardness? Types of water hardness: Generally speaking, water has two hardnesses: temporary hardness and hardness. The sum of the two hardnesses is the total hardness of water. 1. Temporary hardness: If we add lime water (that is, calcium hydroxide, Ca(OH)2) into hard water, or boil hard water, and the hardness decreases, we say that these decreased hardness is called“ Temporary hardness”. These methods will make calcium, magnesium, bicarbonate (HCO3−) and other substances that make the water hard run away, or settle into solid substances. 2. Hardness: The hardness produced by sulfate or chloride (chloride) containing calcium ions or magnesium ions is called hardness. Although these hardnesses cannot be reduced by boiling and adding lime, they can be reduced by other methods such as ion exchange. Changes in Hardness: If water flows over lime, hardness increases; if water flows over peat, hardness decreases. How to test the hardness in water? To detect the hardness in water, it can be detected by the T8000-WH online hardness analyzer in water. This product is a maintenance-free online monitor based on years of research on water quality analysis products. Suitable for water softening monitoring, reverse osmosis system, filtration and demineralization process control, widely used in pharmaceutical, steel, semiconductor industries. The pretreated water sample is injected into a special reactor by a syringe pump for pretreatment of the water sample. The reacted water sample is detected by a highly selective synthetic substance and a special sensor. Signal, according to the degree of electrical change, the degree of hardness in the water sample can be calculated.