Add an appropriate acidic reagent to the water sample to adjust the pH to an appropriate range, ensuring ferrous ions exist in their dissolved state. Under acidic conditions, ferrous ions undergo complexation reactions with the added chromogenic agent, forming colored complexes. The color depth of this complex is proportional to the concentration of ferrous ions. After the chromogenic agent reacts with ferrous ions, the resulting colored complexes form stable colors in water. The depth of this color directly reflects the concentration of ferrous ions in the water sample. Based on pre-established calibration curves or standard curves, the measured absorbance value is converted into ferrous content. By precisely controlling the amount of reagent added and reaction conditions, combined with advanced measurement technology, accurate measurement of ferrous content in water samples can be achieved.