California · small ground water systems
California chlorine residual requirements
Short answer
California adopts the federal Ground Water Rule for ground water systems, and State Water Board guidance suggests a free chlorine range of 0.2 to 1.0 mg/L in most distribution systems, never over 4.0 mg/L at the first connection. Community and non-transient systems that chlorinate measure the residual with every coliform sample and report quarterly. Many small systems are overseen by their county rather than the State Board.
- Minimum residual
- Guidance target 0.2–1.0 mg/L free in distribution; 4.0 mg/L maximum
- How often
- With each coliform sample; daily recommended in guidance
- Report
- Quarterly residual report within 10 days after the quarter
Who has to chlorinate
- Ground water systems follow the federal Ground Water Rule, adopted by reference. 22 CCR 64430
Minimum residual
- State guidance: target 0.2 to 1.0 mg/L free chlorine in the distribution system for most systems, and never over 4.0 mg/L at the first service connection. State Water Board
Maximum
- 4.0 mg/L chlorine. The residual rules apply to community and non-transient systems; transient systems only for chlorine dioxide. 22 CCR 64533.5
How often to test
- Community and non-transient systems: at the same points and times as total coliform samples. 22 CCR 64534.4
- Guidance: frequency is set case by case, and daily measurement is recommended. State Water Board
Test kits and methods
- Field residual tests must be done by trained personnel. 22 CCR 64415
- Guidance: use the DPD method; a pool test kit is not acceptable. State Water Board
Reporting
- Systems report disinfectant residuals within 10 days after each quarter: samples per month, monthly averages, running annual average and whether the maximum was exceeded. 22 CCR 64537
How long to keep records
- Guidance: keep operational records and chlorine residual results on site at least three years. State Water Board
Parks, campgrounds and seasonal systems
- Systems with 200 or fewer service connections are often overseen by a local primacy agency, such as the county health department, rather than the State Board. State Water Board
Keeping the log in California
Write the range your system's permit or local agency expects at the top of the log. The State Board's own chlorination log template is meant to be kept on file for inspection; any log you keep should hold the same things: date, time, location, result and who took 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
- 22 CCR 64430 — Ground Water Rule requirements
- State Water Board — Chlorination guidelines for small water systems
- 22 CCR 64533.5 — Maximum residual disinfectant levels
- 22 CCR 64534.4 — Disinfectant residual monitoring
- 22 CCR 64415 — Laboratory and field testing personnel
- 22 CCR 64537 — Disinfectant residual reporting
- State Water Board — Local primacy agencies
Last reviewed September 28, 2026. Rules change and states add their own; confirm with your state drinking water program.