Chlorine Monitoring - PUB2730

The Importance of Monitoring Free and Total Chlorine

Public health is protected when public drinking water systems properly disinfect with chlorine and sufficiently monitor for free and total chlorine residuals. These two measures decrease the risk of public exposure to E. coli and other pathogens. In addition, they reduce the liability of water systems as well as the potential need for boil water orders and other public notice requirements. However, the importance of one measure does not outweigh the other. The department’s data shows drinking water systems that chlorinate are far less likely to issue boil order notices when they monitor chlorine routinely and maintain residuals at required levels. All systems that add chlorine are required to measure chlorine residuals. Refer to 10 CSR 60-4.080 for frequency.

Drinking water systems required to chlorinate include:

• Systems supplied by surface water or groundwater under the direct influence of surface water.
• Systems with treatment plants that remove iron and/or soften with lime.
• Compliance monitoring systems required to provide 4-log virus inactivation under 10 CSR 60-4.025 Ground Water Rule.
• Community wells built prior to Oct. 1, 1979 and not built according to state construction standards.
• Systems that agreed to chlorinate as part of a compliance monitoring agreement with the department.

Tips for successful chlorination and monitoring of chlorine residuals

• Monitor and record levels of free and total chlorine residuals every day the system provides water to the public.
• Use a department-approved drinking water chlorine test kit for chlorine using the DPD method (check with department staff if unsure). The department does not recognize the use of color comparator test kits for systems reporting chlorine residuals to the department.
• Maintain an adequate supply of DPD reagent and replacement sample cells. Ensure reagent has not expired and cells are not scratched or cloudy.
• Check to make sure that total chlorine residual is greater than free chlorine residual.
• Check that total chlorine consists of at least 80 to 85% free chlorine. If the percentage of free chlorine falls below this level, breakpoint chlorination may not be achieved and the situation may warrant further evaluation.
• Inspect daily the solution tank and the chemical feed pump to ensure an adequate level of chlorine solution and an operational pump.
• To help troubleshoot issues that arise, keep records of solution dosages, solution tank levels, and settings for chemical feed pumps.
• Near the solution tank, keep printed instructions that explain how to fill the tank with fresh chlorine solution and maintain the tank appropriately at the recommended levels of chlorine.
• Become familiar with operation of the instrument, establish a schedule for regular servicing of the chlorination system and keep essential spare parts on-site, or close by, for on-the-spot repairs. (For example: a spare chemical pump)
• Contact the department to receive technical assistance to help further evaluate the situation.

Chlorine residual requirements

• Distribution system entry-point minimum: 0.5 mg/L chlorine or 1.0 mg/L chloramine (A higher level of residual may be required).
• Distribution minimum: 0.2 mg/L total chlorine.
• Maximum residual disinfectant level (MRDL): 4.0 mg/L.
• Keep monthly operating reports of daily chlorine residuals, solution ratios, and pump settings.
• Record free and total residuals on bacteriological sample collection form at the time of each sample.

Please contact a regional office for further information and assistance.

Kansas City Regional Office at 816-251-0700
Northeast Regional Office at 660-385-8000
Southeast Regional Office at 573-840-9750
Southwest Regional Office at 417-891-4300
St. Louis Regional Office at 314-416-2960