■Where do you measure from the faucet? The residual effect of disinfection is confirmed at the end of the water supply faucet. This is to check whether chlorine remains not only at the outlet of the water purification plant but also at the end of the distribution. ■Do you check color and turbidity visually? Color and turbidity are checked through visual inspection. The enforcement regulations state that on the days when color and turbidity tests are conducted, the daily inspections of color and turbidity can be omitted. ■There are six methods for measurement! The national notification specifies the DPD method, current method, spectrophotometric method, continuous automatic measurement device spectrophotometric method, polarographic method, and portable residual chlorine measurement method. ■Procedure for the DPD method Samples are taken in glass bottles and tested immediately. A buffer solution and DPD reagent are added to the water sample to make a total of 50 mL, and the free residual chlorine is determined by comparing the color with a standard colorimetric series. Adding potassium iodide reveals the total residual chlorine, and the difference gives the combined residual chlorine. ■Does any portable measuring device suffice? The notification specifies that the lower limit of quantification must be 0.1 mg/L or less, and it should be able to display up to two decimal places. Regular cleaning and maintenance according to the instruction manual are also required.

What if it falls below 0.1 mg/L? The free residual chlorine that should be maintained in the water from the water supply faucet is above 0.1 mg/L. If there is a possibility of not meeting the standard, a temporary inspection must be conducted, and when there is a risk of harming health, there is an obligation to immediately stop the water supply and inform the relevant parties. Can't just measuring prevent it?! In 2010, there was an incident at a certain simple water supply where the residual chlorine at the end of the water supply remained below 0.1 mg/L for over a month. The measurements entrusted to residents were conducted five days a week, with no inspections at the end on the remaining two days, and the results were reported in a lump sum for the month without verification. Results should be connected daily Daily communication of inspection results to the contractor is also part of the responsibilities of the water supply technical manager. By verifying the measured results every day, abnormalities can be detected quickly. Inspection records must be kept for five years. Confirmation of chlorine agents and injection equipment Sodium hypochlorite and others must ensure effective chlorine concentration while considering storage temperature and duration. Additionally, the injection equipment should be inspected, and the actual injection amount should be confirmed. We also offer consultations on how to select chlorine agents and inspect injection equipment. Please feel free to consult with us first.