All public water systems that add chlorine for the purpose of continuous disinfection are required to monitor the residual disinfectant concentration as described in the chlorination requirements section below.
Detectable Chlorine Residual
With the adoption of the Group A WAC changes in January 2017, detectable residual disinfectant concentration has been defined and must be at least 0.2 mg/L.
No more color wheel for source disinfection compliance. If your system is required to treat to CT6 or 4-log virus inactivation, you must measure free chlorine residual in accordance with an EPA-approved method. A color wheel can't be used to comply with these requirements. A digital colorimeter using an EPA approved method is allowed.
- CT-6 Disinfection: Systems required to provide CT6 disinfection must measure and record the chlorine residual at entry to distribution 5 days/week. Your system must maintain your required minimum free chlorine residual requirement at entry to the system. If you choose to monitor the distribution system residual instead of at the point of entry, your distribution residual must satisfy the entry point residual requirement.
- 4 Log Virus Inactivation: Systems with a confirmed E. coli source are required to provide 4 log virus inactivation. These systems must measure and record the chlorine residual at entry to the distribution 7 days/week. Your system must maintain your required minimum free chlorine residual requirement at entry to the system. If you choose to monitor the distribution system residual instead of at the point of entry, your distribution residual must satisfy the entry point residual requirement. 4 log required systems are also required to complete and submit a Ground Water Rule Monthly Summary Form. Contact your regional office if you need this form.
- Distribution Residual: Systems maintaining a minimum free chlorine residual in distribution. You must measure and record the chlorine residual in distribution 5 days/week.
Types of Violations
All public water systems that chlorinate are subject to the following violations.
Failure to submit your report by the 10th of the following month.
- CT6 treatment: failure to measure free chlorine residual at entry point to the distribution 5 days/week, or each day the disinfected source supplies the distribution system, whichever is less.
- 4 log virus inactivation treatment: failure to measure free chlorine residual at entry point to the distribution each day the disinfected source supplies the distribution system.
- Distribution system residual: failure to measure chlorine residual at representative locations throughout the distribution system 5 days per week.
Treatment technique violation
Failure to meet the required minimum residual at entry or throughout the distribution system.
Chlorination Report Forms
Contact your regional office to receive a customized form including all requirements specific to your system, or you can download a form for your system using the links below.
- For CT6 and 4 log virus inactivation systems, download a source disinfection report form 331-430 Excel | 331-430 Word
- For systems disinfecting their distribution system, download a distribution report form 331-593 Excel | 331-593 Word
Submit your monthly treatment reports by email, mail, or fax to your regional office by the tenth day of the following month.
- Eastern Region
16201 East Indiana Avenue, Suite 1500
Spokane Valley, WA 99216
- Northwest Region
20425 72nd Ave. South, Suite 310
Kent, WA 98032-2358
- Southwest Region
PO Box 47823
Olympia, WA 98504-7823
- Disinfection Byproducts 331-251 (PDF)
- Alternate Disinfectants 331-252 (PDF)
- Chlorination of Drinking Water 331-253 (PDF)
- Contact Time for Small Water Systems 331-343 (Word)
- Chlorine Controls for Small Water Systems 331-398 (PDF)