Issue #4 November 2012

Scope (1)

This bulletin is applicable to regulated Ontario municipal residential large and small drinking water systems (DWS) which provide chlorination for primary and secondary disinfection, and for systems using chloramination for secondary disinfection.

Regulatory Requirements (2)

Primary disinfection

If a DWS provides chlorination for primary disinfection, Schedule 7, section 7-2 (1) of the Regulation requires that free chlorine residual be monitored using continuous monitoring equipment in the treatment process at or near a location where the intended contact time has just been completed. Such analyzers are sometimes referred to as "regulatory" analyzers. The Ministry considers regulatory analyzers to be analyzers that are used for sampling and testing that is required under the Regulation, an Approval, a Drinking Water Works Permit (DWWP), a Municipal Drinking Water Licence (MDWL) or Order, or any other analyzers that may be used to satisfy such requirements.

Secondary disinfection for large municipal residential DWS

If a large municipal residential DWS provides chlorination for secondary disinfection, Schedule 7, section 7-2 (3) of the Regulation requires that at least seven distribution samples be taken each week and tested for free chlorine residual if the system provides chlorination, or combined chlorine residual if the DWS provides chloramination.

Secondary disinfection for small municipal residential DWS

If a small municipal residential DWS provides chlorination for secondary disinfection, Schedule 7, section 7-2 (5) of the Regulation requires that at least two distribution samples be taken each week and tested for free chlorine residual if the system provides chlorination, or combined chlorine residual if the DWS provides chloramination.

Ontario Regulation 170/03, the Drinking Water Systems Regulation (the “Regulation”) made under the Safe Drinking Water Act, 2002 (the “Act”) specifies how operational checks for parameters such as chlorine residual must be conducted in regulated drinking water systems (DWS) using either grab samples or continuous monitoring equipment. Where continuous monitoring equipment is used, the equipment must meet certain minimum requirements and the owner/ operator must follow certain procedures. This bulletin provides information to owners of municipal residential large and small DWS concerning the use of this equipment and is for general information only. It is not intended to provide specific advice or recommendations and is not legal advice. The reader should review the Act and Regulation or consult a lawyer for answers to specific questions.

Continuous Monitoring versus Grab Samples (3)

Continuous monitoring equipment is mandatory when measuring the effectiveness of primary disinfection whereas, taking an appropriate number of grab samples within a distribution system (DBS) satisfies the regulatory requirements for secondary disinfection.

Despite this, DWS owners may choose to install one or more continuous monitoring devices at strategic locations within the DBS to measure residual chlorine levels instead of taking grab samples. Such analyzers would also be considered to be "regulatory" analyzers because they are being used to take distribution samples required by the Regulation. Additional continuous monitoring analyzers may be located in booster stations, re-chlorination facilities, reservoirs, etc., to monitor the re-chlorination process continuously. However, if such analyzers are monitoring treatment processes and are not being used to address requirements under the Regulation or under an Approval, a DWWP, a MDWL or Order, they are considered by the Ministry to be "process" analyzers.

Regulatory Analyzers (4)

Continuous monitoring equipment required by the Regulation to measure primary disinfection and the continuous monitoring equipment chosen by the DWS owners to measure distribution samples (in lieu of taking grab samples) are regulatory analyzers and the analyzers must comply with the requirements contained in Schedule 6 of the Regulation. The requirements in section 6-5 include such factors as sampling frequency, recording test data, alarm standards, review of data 72 hours after testing, etc.

A test result described in Schedule 16, sections 16-3 (1) 4 or 5 of the Regulation from a distribution sample is an adverse test result from a regulatory analyzer and a report under section 18 of the Act must be made. An adverse test result for a regulatory analyzer taking distribution samples is a result that is less than 0.05 mg/L free chlorine for chlorination or less than 0.25 mg/L combined chlorine and 0.05 mg/L free chlorine for chloramination.

A test result from a regulatory analyzer measuring primary disinfection indicating that inadequately disinfected water is being directed to the users of the system is an observation that must be reported under Schedule 16, section 16-4.

Process Analyzers (5)

Process analyzers can be used within a treatment plant (e.g. where analyzers may exist as part of the treatment process control but are not used to measure residual chlorine at the end of contact time) as well as within a DBS. This equipment does not have to meet the requirements specified in Schedule 6 of the Regulation. However, if a process analyzer indicates that inadequately disinfected water is being directed to the users of the system, the observation must be reported under Schedule 16, section 16-4. Example situations may include:

  1. In a re-chlorination facility there can be one or more analyzers; one on the entry line (upstream) measuring residual levels of the incoming water and the second one on the exit line (downstream). The chlorine dose is adjusted based on the upstream analyzer reading. If an online analyzer located on the downstream side displays a value less than 0.05 mg/L for 15 minutes or more, this could mean that improperly treated water is being directed to the users of the DBS. If it is determined that the low readout is not due to mitigating circumstances such as a calibration error, broken probe, electrical power surge, etc., the observation should be reported under section 16-4, Schedule 16.

  2. If a DBS provides chloramination for secondary disinfection, chlorine may be added at the re-chlorination facility in proportion to the levels of residual ammonia present. If the downstream analyzer measures less than 0.25 mg/L combined chlorine and free chlorine less than 0.05 mg/L free chlorine, for 15 minutes or more, this could mean that improperly treated water is being directed to the users of the DBS. If it is determined that the low readout is not due to mitigating circumstances, the observation should be reported under section 16-4, Schedule 16.

  3. The owner of a stand-alone DBS (receiver) not claiming an exemption under section 5(4) of the Regulation is required to fulfill the distribution sampling requirements by taking the requisite number of grab samples. However, in addition to the grab samples, the receiver DBS owner may choose to install continuous monitoring equipment at the point of entry to the DBS. This would be considered to be a "process" analyzer. If the analyzer displays readings below 0.05 mg/L free chlorine for 15 minutes or more and if it is determined that the low readout is not due to mitigating circumstances, the receiver system has the potential of receiving inadequately treated water and the observation should be reported under Schedule 16, section 16-4 of the Regulation.

Relief from Regulatory Reporting Requirements (6)

If the purpose of continuous monitoring equipment installed within a DBS is for process control only and there are valid reasons to believe that a low readout would not necessarily indicate an adverse test result, for example, if there are other explanations such as equipment failure, electrical surge, calibration error, etc., the owner could request relief from reporting requirements under Schedule 16, sections 16-2 (1) (f) or 16-3 (1) 4 or 5 of the Regulation. The Director would assess each situation on a case-by-case basis and, if satisfied that there was no immediate threat to the users of the system, may grant relief from reporting requirements.

Municipal Water Drinking License and DWWP (7)

Despite a DWS having hundreds of separate monitoring instruments, it would be impractical to list all of them on a DWWP since changes to any of the listed instruments would require an amendment to the control document.

As such, the Ministry does not list instrumentation as part of the Works description unless there is a compelling reason for doing so. It is important to note that not all continuous monitoring equipment described in a DWWP is necessarily a "regulatory" analyzer. The DWS owner/operator should decide which equipment will be designated as regulatory analyzers, and which equipment will be designated as process analyzers.

The MDWL requires the system owner to maintain an up-to-date operations and maintenance manual on-site. The manual should specify which analyzers will be used as regulatory analyzers at a particular site, as well as which equipment will be designated as process analyzers (i.e. analyzers that will be used for process monitoring both within the DBS as well as in the treatment plant). The information recorded in the operations manual must be kept up-to-date and made available during a Ministry inspection.

Updated: July 29, 2021
Published: November 18, 2015