>> Questions or Comments: pdws@tceq.texas.gov
You are here:

Public Water Systems Using Chlorine Dioxide or Ozone

If public water systems use chlorine dioxide or ozone, they must comply with additional disinfectant and monitoring rules.

Chlorine Dioxide and Chlorite

Chlorine dioxide can be used in the treatment of drinking water to improve taste, odor, and color, remove iron and manganese, and inactivate chlorine resistant microorganisms. Systems may choose to use chlorine dioxide because it's less likely to form DBPs in comparison to free chlorine. All systems that use chlorine dioxide must monitor for chlorine dioxide and chlorite.

Ozone and Bromate

Bromate is a DBP that can form when ozone is used on water containing bromide. All community and non-transient, non-community public water systems that use ozone must monitor for bromate.

Monitoring Frequency of Analytes by Water System Location

Treatment Sampling Location Monitor For Frequency
Chlorine Dioxide Entry Point Chlorine Dioxide Daily
Chlorine Dioxide Entry Point Chlorite Daily
Ozone Entry Point Bromate Monthly
Chlorine Dioxide Distribution Chlorine Dioxide In the event of a daily exceedance
Chlorine Dioxide Distribution Chlorite Monthly and in the event of a daily exceedance

Systems Using Chlorine Dioxide

Monthly monitoring

Monthly chlorite monitoring in the distribution system requires a three-sample set for every entry point providing chlorine dioxide treated water. Collect samples from:

  1. a location near the first customer;
  2. a location representative of the average residence time; and
  3. a location representative of the maximum residence time.

Each set must be collected when chlorine dioxide is in use and on the same day.

Daily Monitoring

All systems that use chlorine dioxide must monitor daily for chlorine dioxide and chlorite at the entry point. For any daily chlorine dioxide level that exceeds 0.8 mg/L, systems must collect three chlorine dioxide samples in the distribution system.

Sample Locations and Timing

If you have a chlorination facility in the distribution system, sample:

  1. the service connection nearest the treatment plant two hours after the exceedance,
  2. the first service connection after the point where water is re-chlorinated 6 hours after the exceedance, and
  3. near the end of the distribution system 8 hours after the exceedance.

If you don't have a chlorination facility in the distribution system:

Additional samples must be taken at the service connection nearest the treatment plant at two-, six-, and eight-hour intervals.   

Daily chlorite and chlorine dioxide samples must be analyzed at an approved facility. Contact the Drinking Water Quality Team at (512) 239-4691 to check your status as an approved facility. You can find the approval form at Public Water System Monitoring Plans.  

Monthly chlorite samples, the three sample set(s), must be analyzed at an accredited facility. Check Drinking Water Watch to ensure TCEQ has the correct chlorite distribution locations.  

Violations

Chlorine Dioxide MRDL 

If your system exceeds 0.8 mg/L on a daily chlorine dioxide sample, and:

  • if follow-up chlorine dioxide samples are not collected = Acute maximum residual disinfectant level (MRDL),
  • if chlorine dioxide samples are collected and any sample is over 0.8 mg/L = Acute MRDL,
  • chlorine dioxide samples are collected and none exceed 0.8 mg/L = Non-acute MRDL
Chlorite MCL

The average of the three sample set exceeds 1.0 mg/L = a chlorite maximum contaminant level violation.

Bromate MCL 

If, at the end of any quarter, the running annual average of monthly averages, computed quarterly, exceeds 0.010 mg/L bromate = bromate MCL violation.

Monitoring and Reporting Violation
  • Failure to monitor for bromate, chlorine dioxide, or chlorite,
  • Failure to mail the chlorine dioxide monthly operating report (CLO2 MOR) and distribution chlorite results to TCEQ by the tenth day of the month following the end of the monitoring period, or
  • Failure to mail bromate results to TCEQ by the tenth day of the quarter following the end of the monitoring period.

Reporting Requirements

Mail the CLO2 MOR and distribution chlorite results to TCEQ by the tenth day of the following month. Systems that did not use chlorine dioxide for one month are still required to mail a CLO2 MOR. The CLO2 MOR can be found at Forms, Instructions, and Guidance for Surface Water Monthly Operating Reports

Mail bromate results to TCEQ on the tenth day of the month following the end of the quarter.

Send to: 

Regular mail:

Certified mail:
TCEQ
MC-155, Attn: Chlorine Dioxide or Bromate
PO BOX 13087
Austin, TX 78711-3087

 

TCEQ
MC-155, Attn: Chlorine Dioxide or Bromate
12100 Park 35 Circle
Austin, TX 78753


All requirements listed above can be found in Standards and Reporting Requirements for Public Water Systems (TCEQ RG-346).

To see chlorite and bromate results visit Drinking Water Watch.

For help navigating the website please contact the Drinking Water Quality Team at (512) 239-4691 or PWSChem@tceq.texas.gov.