Pennsylvania · small ground water systems
Pennsylvania chlorine residual requirements
Short answer
Pennsylvania requires community water systems to disinfect ground water continuously, keep at least 0.40 mg/L free chlorine at each ground water entry point, and keep at least 0.2 mg/L in the distribution system. Small systems take a daily entry-point grab sample during peak flow and check the distribution system at least weekly and with every coliform sample.
- Minimum residual
- 0.40 mg/L free at the entry point; 0.2 mg/L in distribution
- How often
- Entry point daily (≤3,300 people); distribution weekly plus with coliform samples
- Report
- Results within 10 days after the month; monthly operational report kept on file
Who has to chlorinate
- Community water systems must provide continuous disinfection of ground water sources. 25 Pa. Code §109.202
- Non-community ground water systems aren't required to disinfect unless corrective action requires it. 25 Pa. Code §109.1302
Minimum residual
- Each ground water entry point: at least 0.40 mg/L free chlorine or its equivalent, unless DEP approves another minimum. 25 Pa. Code §109.1302
- Distribution system: at least 0.2 mg/L, measured as free chlorine for systems using chlorine. 25 Pa. Code §109.710
- Non-transient and transient systems that installed chemical disinfection under the ground water rules must also meet the 0.2 mg/L distribution minimum. 25 Pa. Code §109.710
- A ground water system collecting fewer than 40 samples a month complies as long as no more than one sample a month is below the minimum for two consecutive months. 25 Pa. Code §109.710
Maximum
- Pennsylvania adopts the federal MRDLs, including 4.0 mg/L for chlorine. 25 Pa. Code §109.202
How often to test
- Entry point, systems serving 3,300 or fewer: a daily grab sample during the hour of peak flow. If it's below the minimum, follow-up samples every 4 hours. 25 Pa. Code §109.1305
- Distribution system: at the same time and place as each total coliform sample, and at representative locations at least once a week. 25 Pa. Code §109.301
Test kits and methods
- Residuals may be measured by a certified operator, or by someone following a standard operating procedure under DEP's rules. 25 Pa. Code §109.304
- DEP's operator workbook says results should not be rounded, and approved digital analyzers should read to two decimal places. PA DEP
Reporting
- Results are reported within 10 days after the month the result is received or the monitoring period ends, whichever is shorter. 25 Pa. Code §109.701
- For entry-point monitoring, report the date, time and lowest value each day the residual stays at or above the minimum. 25 Pa. Code §109.1307
- DEP's workbook directs distribution residuals to the SDWA-1 form, submitted electronically by the 10th of the following month. PA DEP
- Operators prepare a monthly operational report on DEP forms, keep it on file at least 2 years, and submit it on request. 25 Pa. Code §109.701
How long to keep records
- Performance monitoring records (other than turbidity): at least 3 years. 25 Pa. Code §109.701
- Lowest daily entry-point residuals: at least 5 years; the DEP-specified minimum residual: at least 10 years. 25 Pa. Code §109.1307
Parks, campgrounds and seasonal systems
- Seasonal systems (many campgrounds) must certify completion of a DEP-approved start-up procedure in writing before serving water each season. 25 Pa. Code §109.715
Keeping the log in Pennsylvania
Pennsylvania's numbers are among the strictest for ground water systems, and daily entry-point readings mean a daily log. Record the value exactly as the analyzer shows it, to two decimal places, and keep the lowest reading of each day easy to find, because that's what gets reported.
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
- 25 Pa. Code §109.202 — State MCLs, MRDLs and treatment technique requirements
- 25 Pa. Code §109.1302 — Ground water treatment requirements
- 25 Pa. Code §109.710 — Disinfectant residual in the distribution system
- 25 Pa. Code §109.1305 — Ground water compliance monitoring
- 25 Pa. Code §109.301 — General monitoring requirements
- 25 Pa. Code §109.304 — Measurement of residuals by certified operators or under an SOP
- PA DEP — Disinfection Requirements Rule operator training workbook
- 25 Pa. Code §109.701 — Reporting and recordkeeping
- 25 Pa. Code §109.1307 — Ground water reporting and recordkeeping
- 25 Pa. Code §109.715 — Seasonal systems
Last reviewed September 28, 2026. Rules change and states add their own; confirm with your state drinking water program.