Page 8: Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing

5.0 Rationale

The use of domestic reclaimed water in residential or commercial locations can help reduce water consumption in Canada. However, the presence of pathogenic microorganisms (bacteria, protozoa and viruses) and some chemicals in domestic wastewater may pose a health risk if the wastewater is improperly treated or if it is used for purposes other than toilet or urinal flushing. Although effective treatment can produce domestic reclaimed water that is virtually free of disease-causing microorganisms, a small number of pathogenic organisms may still be present and pose some risk, such as in the case of accidental cross-connections between the reclaimed system and the drinking water system.

Consequently, it is necessary to ensure that the use of reclaimed water does not pose a risk to the health of Canadians. These guidelines provide guidance to ensure that the risks associated with domestic reclaimed water are addressed through adequate treatment and management processes.

The guideline values for domestic reclaimed water quality have been established to protect public health from microbiological contaminants. There are minimal health impacts expected from chemicals in domestic reclaimed water used only for toilet and urinal flushing. Effective operation of the treatment system is essential for minimizing health impacts from microbiological pathogens. The guidelines include values for several water quality parameters that have been selected because they can demonstrate the effective operation of the treatment system, including disinfection.

On-site reclaimed water systems could include collection and treatment of water from single domestic dwellings or from clusters, such as apartment buildings. Although they will impact fewer people than large systems, their processes may have a complexity similar to that of larger systems. The potential health risks associated with decentralized domestic reclaimed water treatment systems mean that there is a need for a high level of treatment reliability and oversight. The guidance provided in this document also includes information concerning management programs for domestic reclaimed water systems.

It is recommended that authorities develop and implement management programs, giving due consideration to the protection of public health, water quality guidelines, regulatory authority capacity, administrative and operational capacity, and the local political, social and economic climate. The management program would include an initial risk assessment to determine the appropriate levels of microbiological inactivation needed for the system and identify treatment technologies that can consistently achieve the guideline levels established in this document. Operational oversight, inspections and ongoing monitoring should form key components of a management program to ensure that treatment of reclaimed water is effective on a long-term basis. Once effluent water quality parameters are verified upon start-up, it may be appropriate for ongoing monitoring to be based on robust secondary parameters, such as motor performance, fluid pressure, temperature and flow, in addition to real-time monitoring of chlorine residuals or turbidity with sensors that do not require frequent calibration. Verification of effluent water quality could be conducted on a periodic basis (e.g., biannually) and whenever the operational parameters show change in the system.

It is recommended that provinces and territories use this document as a basis for establishing their own requirements or options for the use of reclaimed water in their area of jurisdiction.

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