Water Treatment Plant Operator how-to
How to Measure Chlorine Residual with a Colorimeter
Chlorine residual testing confirms water stays disinfected. Follow your plant’s approved method and instrument instructions.
Chlorine residual testing confirms water stays disinfected. Follow your plant’s approved method and instrument instructions. In short: collect; rinse; zero, then complete the remaining steps below.
Step by step
Collect the sample from the correct tap after flushing as required.
Rinse the sample cell with sample water, then fill to the line.
Zero the colorimeter with the blank sample.
Add the DPD reagent and mix as directed.
Read the result within the time specified by the method.
Record the value, time, location and your initials.
Report results outside target ranges and adjust dosing per procedure.
Safety reminders for water treatment plant operators
- Wear PPE and use proper procedures when handling chlorine and other chemicals
- Follow confined-space entry procedures for tanks, vaults and wet wells
- Lock out pumps and equipment before maintenance
- Stay current on vaccinations and hygiene when working with wastewater
Key terms
Coagulation · Flocculation · Sedimentation · Filtration · Disinfection · Chlorine residual: see the full water treatment plant operator glossary.