Missouri · small ground water systems
Missouri chlorine residual requirements
Short answer
Missouri requires only some ground water systems to disinfect: 4-log compliance systems, iron-removal plants, some older community wells and systems under a compliance agreement. Those systems keep at least 0.5 mg/L free chlorine at the entry point and 0.2 mg/L total chlorine in the distribution system. Systems that chlorinate voluntarily check the entry point Monday to Friday, and DNR doesn't accept color comparators.
- Minimum residual
- Required systems: 0.5 mg/L free at entry; 0.2 mg/L total in distribution
- How often
- Required: daily at entry. Voluntary: Mon–Fri. All: with coliform samples
- Report
- MO 780-2094 by the 10th (4-log systems); others keep records on file
Who has to chlorinate
- DNR lists who must chlorinate: surface water systems, iron removal and lime softening plants, 4-log compliance monitoring systems, community wells built before October 1, 1979 that don't meet state construction standards, and systems under a compliance agreement. Missouri DNR PUB2730
Minimum residual
- Entry point (systems required to disinfect): not less than 0.5 mg/L free chlorine, or 1.0 mg/L chloramines, for more than four hours. 10 CSR 60-4.055
- Distribution system: measured as total or combined chlorine, not below 0.2 mg/L in more than 5% of samples each month for two consecutive months. 10 CSR 60-4.055
- DNR generally treats any measured residual below 0.2 mg/L as non-detectable. MO 780-2094
Maximum
- 4.0 mg/L chlorine (as Cl2). 10 CSR 60-4.055
How often to test
- Systems required to disinfect: a daily entry-point residual. 10 CSR 60-4.080
- Systems that chlorinate but aren't required to: entry point Monday through Friday, excluding federal holidays and days not serving water. 10 CSR 60-4.080
- Every system that adds chlorine: with each total coliform sample. 10 CSR 60-4.080
- DNR's guidance: monitor and record free and total chlorine residuals every day the system provides water. Missouri DNR PUB2730
Test kits and methods
- Use a department-approved DPD test kit. DNR does not recognize color comparator kits for residuals reported to the department. Missouri DNR PUB2730
Reporting
- 4-log ground water systems file MO 780-2094, the Monthly Compliance Monitoring Report, by the 10th of the following month. MO 780-2094
- Other ground water systems required to disinfect keep the information on file instead of submitting it. 10 CSR 60-4.055
- DNR asks systems to keep monthly operating reports of daily residuals, solution ratios and pump settings. Missouri DNR PUB2730
How long to keep records
- Operational analyses: at least 5 years. 10 CSR 60-9.010
- Lowest daily residuals for 4-log systems: at least 5 years; minimum-residual records: at least 10 years. 10 CSR 60-9.010
Parks, campgrounds and seasonal systems
- Seasonal systems complete a start-up procedure and certification (form MO 780-2607) that includes checking disinfectant residuals. Missouri DNR PUB2622
Keeping the log in Missouri
Missouri's guidance asks for free and total chlorine every day, along with solution ratios and pump settings. That's a daily log with a few more columns than a bare chlorine sheet. Record both chlorine values, and note any change to the feed pump or solution on the day you make it.
Print a dated month with the chlorine residual log sheet, or build a sheet for your whole round with the daily water system log sheet.
Other states
For federal rules and every state's program, see chlorine residual requirements.
Sources
- Missouri DNR PUB2730 — Chlorine monitoring
- 10 CSR 60-4.055 — Disinfection requirements
- MO 780-2094 — Monthly Compliance Monitoring Report for Groundwater Systems
- 10 CSR 60-4.080 — Operational monitoring
- 10 CSR 60-9.010 — Records
- Missouri DNR PUB2622 — Seasonal system start-up
Last reviewed September 28, 2026. Rules change and states add their own; confirm with your state drinking water program.