Page 3: Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing

Executive summary

The Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing have been developed as an option to reduce water consumption, in response to the growing interest in water conservation in Canada. The use of domestic reclaimed water can make significant contributions to reducing water use. However, domestic reclaimed water must be treated and managed effectively, as there is a potential health risk to users, particularly from pathogens that can be responsible for severe gastrointestinal illness. Although the long-term goal is to develop comprehensive guidelines to allow the safe use of reclaimed water for many beneficial purposes, the focus of this version of the guidelines is limited to the specific end use of toilet or urinal flushing.

This document provides guidelines for domestic reclaimed water quality, as well as guidance on potential elements of a management framework (Part I) and an overview of the scientific basis for the guidelines (Part II). It recommends possible elements of a management framework that are applicable to on-site or decentralized treatment of domestic water for reuse in residential or commercial toilet and urinal flushing. Plumbing requirements for non-potable water systems are addressed by CSA Standard B128.1-06/B128.2-06, Design and installation of non-potable water systems/Maintenance and field testing of non-potable water systems (CSA, 2006).

The objective of establishing guidelines for domestic reclaimed water is to ensure that the operation of water reclamation systems is protective of public health. Consequently, the guidelines include values for several water quality parameters that have been selected because they can demonstrate the effectiveness of treatment on an ongoing basis.

These guidelines are intended for use by regulatory authorities, public health professionals, engineering consultants and others with a technical understanding of the subject area.

Health effects

There are situations where the use of domestic reclaimed water to flush toilets (and urinals in commercial buildings) can make significant contributions to reducing water use. 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. This can lead to ingestion of water containing human enteric pathogens that can cause severe gastrointestinal illness. This is of particular concern for susceptible individuals, such as infants, the elderly and those who have compromised immune systems, for whom the effects may be more severe, chronic (e.g., kidney damage) or even fatal. Users of domestic reclaimed water for toilet and urinal flushing may also accidentally ingest very small volumes of water through aerosols or hand-to-mouth contact with droplets.

Exposure to chemicals from the domestic reclaimed water is expected to be minimal when compared with other domestic exposures. Consequently, the health impacts from exposure to chemicals in domestic reclaimed water used only for toilet and urinal flushing are also expected to be minimal.

Management framework

Management of on-site reclaimed water systems is of particular importance. Such systems could include collection and treatment of water from single domestic dwellings or from clusters, such as apartment buildings. Although they will affect fewer people than will large systems, small systems, from a process perspective, 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.

It is recommended that authorities develop and implement a management program for domestic reclaimed water systems, giving due consideration to the protection of public health, local administrative and operational capacity, and economic considerations. A site-specific risk assessment should be conducted initially to determine the appropriate levels of microbiological reduction or inactivation needed for the specific system. Treatment technologies used should 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.

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