Take proper amount of water sample in the conical flask, use demineralized water to dilute to 100mL, add 2 ~ 3 drops of phenolphthalein indicator, at this moment, if the solution is in red color, use 0.005 mol/L diluted sulfuric acid solution for neutralization  until the  solution turns to colorless; If the color doesn't appear red color, use NaOH solution for neutralization to reddish， then add dilute sulphuric acid solution for titration to make the color become colorless . then add 1 ml10 % of potassium chromate indicator. At last , add T = 1 mg/mL of AgNO3 standard solution for titration to make the solution become orange. Records the consumed AgNO3 standard solution volume a, and then conduct  blank test at the same time, record the consumption volume of silver nitrate standard solution b, the calculation formula is as follows:
                              (a-b)×T
        Chlorine=                          ×1000  mg/L
                                    V
a - representing the volume of AgNO3 solution for titration, mL.
T - showing the titer of AgNO3, mg/mL.
V - showing the volume of water samples taken, mL.