This Standard specifies the determination method for hardness of water used in boiler and cooling system. This Standard applies to the determination for hardness of water used in boiler and cooling system. The determination range of chrome black T method in this Standard is 0.01mmol/L~5mmol/L. When it exceeds 5mmol/L, the sampling volume can be appropriately reduced. Determine after dilution. The determination range of acid chrome blue K method is 1¦Ìmol/L~100¦Ìmol/L. The determination range of potentiometric titration is 0.25mmol/L~10mmol/L (both with Ca2+ and Mg2+ as basic units). This Standard is also applicable to the determination of the hardness of natural water, cooling water, demineralized water and boiler feed water.