Guidance on the use of Enterococci as an Indicator in Canadian Drinking Water Supplies
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Organization: Health Canada
Date published: 2020-06-26
Health Canada
Ottawa, Ontario
June 2020
This document may be cited as follows:
Health Canada (2020). Guidance on the Use of Enterococci as an Indicator in Canadian Drinking Water Supplies. Water and Air Quality Bureau, Healthy Environments and Consumer Safety Branch, Health Canada, Ottawa, Ontario. (Catalogue No. H144-68/2020E-PDF).
The document was prepared in collaboration with the Federal-Provincial-Territorial Committee on Drinking Water of the Federal-Provincial-Territorial Committee on Health and the Environment.
Any questions or comments on this document may be directed to:
Water and Air Quality Bureau
Healthy Environments and Consumer Safety Branch
Health Canada
269 Laurier Avenue West, Address Locator 4903D
Ottawa, Ontario
Canada K1A 0K9
Tel.: 1-833-223-1014 (toll free)
Fax: 613-952-2574
E-mail: hc.water-eau.sc@canada.ca
Other Guideline Technical Documents for the Guidelines for Canadian Drinking Water Quality can be found on the following web page: www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/water-quality.html
Part A. Guidance on the use of Enterococci as an indicator in Canadian Drinking Water Supplies
A.1 Goal
The intent of this document is to provide provinces, territories, other government departments and stakeholders (such as water system owners and laboratories) with guidance on how the enterococci group of organisms can be used as an indicator in drinking water monitoring programs.
A.2 Background
In drinking water monitoring programs, indicator organisms are used to assess the microbiological safety of water as the direct detection of pathogenic organisms remains impractical. Globally, E. coli is widely utilized as the first indicator of choice for detecting fecal contamination in drinking water. Using E. coli as the primary indicator of fecal contamination along with total coliforms as a general indicator of microbial water quality contamination, is part of an internationally accepted approach for verifying that drinking water has been adequately treated. However, E. coli is more sensitive to environmental stresses and drinking water disinfectants than many types of bacteria, viruses and protozoa; and therefore the absence of E. coli does not necessarily indicate the absence of these microorganisms. Thus, the use of alternative or additional indicators has been explored by the drinking water industry to provide additional information on water quality. The enterococci group of organisms is one of these indicators.
A.3 Using enterococci in assessing drinking water quality
Enterococci have been used as fecal indicator bacteria for assessing the quality of recreational water, drinking water and water re-use applications in many parts of the world. They are a hardy group of bacteria that provide a strong indication of fecal contamination and are somewhat more resistant to environmental stresses and drinking water disinfectants than E. coli.
Enterococci, like E. coli can be used in drinking water monitoring programs to provide additional information on:
- the quality of the drinking water source;
- the adequacy of drinking water treatment; and
- the microbial condition of the distribution system.
Some groundwater and distribution system monitoring programs in North America and internationally have shown that enterococci are useful as a supplemental indicator, providing better insight into fecal contamination events in vulnerable systems. Given their greater persistence, enterococci may be detected in cases where E. coli is not. Therefore, enterococci can be considered for microbial indicator monitoring in drinking water systems that are suspected of being susceptible to fecal contamination but where E. coli has not been found or has been detected very infrequently.
Enterococci testing may be useful in the following scenarios:
- monitoring programs for groundwater sources that are vulnerable to fecal contamination (e.g., as determined by source water assessments, historical microbiological data, or for systems not meeting the minimum 4 log goal for the removal and/or inactivation of enteric viruses).
- monitoring programs following water mains disinfection procedures for water utilities frequently experiencing disruptions in their drinking water distribution system (e.g., repeated mains breaks or pressure losses).
For other areas such as surface water sources and drinking water immediately post-treatment or leaving the treatment plant, the data is less clear about significant differences in the survival and detection of enterococci and E. coli.
Water utilities considering the use of enterococci need to be aware of the limitations of this group of indicators, including their detection in more non-fecal habitats than E. coli; and the very limited comparative detection data. Until more data are available, it is recommended that enterococci be viewed as a complementary indicator of fecal contamination. Combining multiple indicators affords a better understanding of changes in microbial water quality, and increases the likelihood of detecting periods of higher risk to human health; this is an approach supported by the drinking water literature.
Decisions regarding including enterococci as a monitoring parameter in a regulatory or legislative context should be made by the responsible drinking water authority in cooperation with drinking water utilities. Individual water utilities considering conducting voluntary monitoring for enterococci should base their decisions on a system-specific assessment. Utilities should also consult with the responsible drinking water authority to confirm system-specific requirements and necessary corrective action should enterococci be detected (see A.4).
A.4 Monitoring considerations
Authorities and water utilities need to be aware that fecal indicator bacteria are used to provide a check of the performance of the barriers in place for the production of safe drinking water. They are not intended to serve as a rapid indicator of system operational issues, but they can alert water utilities to serious water quality problems that require action. Ideally, water utilities wishing to further achieve their objective of minimizing risk and assuring drinking water quality should focus their strategies on process management improvements. For example, the development of a water safety plan can help identify priority drinking water system hazards and risks as well as the monitoring tools needed for verifying that the system is delivering drinking water of the desired level of quality.
For any drinking water system, sampling frequency will vary based on the goals of the monitoring program as discussed in B.3.3. The presence of enterococci provides evidence of the potential vulnerability of the source water or treated and distributed water to fecal contamination. Detection should lead to further action including an evaluation of potential sources or causes and of the capability of the barriers in place to achieve safe-drinking water. When enterococci are detected in a drinking water sample, confirmation, notification and corrective actions similar to those outlined in the guideline technical document for E. coli should be put in plac.....
B.2.4 Role of enterococci as an indicator
The adoption of a risk-based approach, such as a source-to-tap or a water safety plan approach, is essential to the effective management of drinking water systems (CCME, 2004; WHO, 2017; Health Canada, 2013; Government of Alberta, 2015). Current Canadian drinking water guidelines encourage the adoption of a source-to-tap approach to produce clean, safe, and reliable drinking water. This approach includes the protection of source water, the use of appropriate and consistently effective treatment, a well-maintained distribution system, qualified personnel, routine verification of drinking water quality, and communication and public education.
E. coli and total coliforms are bacterial indicators that are used to verify water safety and changes in water quality, respectively. Enterococci are an additional bacteriological indicator of fecal contamination that can also be used under a source-to-tap approach to demonstrate that the drinking water system is producing water that is microbiologically acceptable. Support for the use of multi-indicator approaches for verifying drinking water quality is provided in the literature (WHO and OECD, 2003; WHO, 2005, AWWA, 2017).
The current understanding is that enterococci are a less fecal-specific indicator of contamination compared to E. coli (WHO and OECD, 2003; Byappanahalli et al., 2012a; Jang et al., 2017). However, the enterococci group of organisms possess characteristics that provide advantages when used as a fecal contamination indicator. Studies have shown that enterococci are somewhat more resistant to disinfectants commonly used in the drinking water industry when compared to E. coli (see Section B.4). Enterococci have also been shown to survive better and therefore be transported further than E. coli and thermotolerant coliforms in certain environments (e.g., marine waters, groundwater) (Keswick et al., 1982; Bitton et al., 1983 Sinton and Donnison, 1994; Naclerio et al., 2008; Schneeberger et al., 2015). Thus, because of their longer persistence, enterococci may be detected in cases where E. coli has not been detected.
Any decisions regarding including enterococci as a monitoring parameter in a regulatory or legislative context should be made by the responsible drinking water authority in cooperation with drinking water utilities. For water utilities, the decision to monitor for enterococci should be informed by a system-specific assessment.
It is important for water utilities to remember that the purpose of routine monitoring for bacteriological indicators is to provide a check that the drinking water system is under control and performing adequately. Indicator detection can alert water utilities to serious water quality problems that require further evaluation and action. However, they are not intended to serve as a rapid indicator of system operational issues. Information from all routine operational monitoring parameters (e.g., bacteriological indicators, disinfection measurements, turbidity) should be used together to inform assessments of drinking water safety and to support decision making.
B.2.4.1 Source water monitoring
For surface water sources, data suggests that enterococci would not provide a more sensitive indication of fecal contamination or pathogen presence than E. coli (Brookes et al., 2005; Wilkes et al., 2009, Yard et al., 2014).
For groundwater sources, evidence suggests that wells identified as being susceptible to fecal contamination (e.g., via source water assessments or historical data) are a setting where adding enterococci into a monitoring plan may provide benefits. Data from monitoring programs for groundwater showed that enterococci testing indicated additional instances of fecal contamination that were not captured by E. coli testing (Payment and Locas, 2005; MDDELCC, 2016). Fout et al. (2017) also found that enterococci may be a more successful predictor of wells vulnerable to pathogen contamination than E. coli in hydrogeologically susceptible settings.
Detection of enterococci in a groundwater well indicates the presence of a possible pathway for fecal contamination. Further actions should include an evaluation of the barriers in place to achieve safe-drinking water and the consideration of corrective actions for non-disinfected systems and systems unable to meet disinfection requirements in place.
B.2.4.2 Treated and distributed water monitoring
Enterococci are somewhat more resistant to drinking water disinfectants that E. coli, but both are readily inactivated at doses recommended for drinking water disinfection. (See Section B.4). The available data is not sufficient to show that enterococci testing of water immediately after treatment or leaving the treatment plant would provide significantly improved information over other indicator testing on treatment effectiveness.
With respect to distribution system monitoring, the evidence to date suggests that enterococci may be a useful indicator of post-treatment contamination (Mendez et al., 2004; Batté et al., 2006; KWR, 2012, European Commission, 2015; DWI, 2016; DWQR, 2016b). Datasets from distribution system monitoring programs and full-scale studies have demonstrated that the frequency of detection of enterococci can be greater than for E. coli (Mendez et al., 2004; Batté et al., 2006; KWR, 2012; DWI, 2016; DWQR, 2016b EPA, 2016a, 2016b). Monitoring programs for determining water quality following the disinfection of newly installed or repaired water mains are one particular area where adding enterococci testing may be valuable (WHO and OECD, 2003). Some standards governing the installation of drinking water require enterococci testing following the disinfection of new pipelines (BNQ, 2018).
Well-designed, operated and properly maintained treatment and distribution systems should consistently produce drinking water with no detectable enterococci. Therefore, the presence of enterococci in treated, distributed water indicates inadequate treatment or post-treatment contamination. Further actions should include a response similar to that recommended for E. coli. This can include notification, corrective actions and the use of boil water advisor
B.4 Treatment considerations
The primary goal of treatment is to reduce the presence of disease-causing organisms and associated health risks to an acceptable or safe level.
There has been limited data published on the effectiveness of various drinking water treatment technologies (i.e. filtration or disinfection processes) specific to the removal and inactivation of enterococci. Overall, physical removal methods (including coagulation, flocculation, sedimentation, slow or rapid sand filtration and direct filtration with or without filtration aid) can accomplish 1–4 log removal of indicator organisms (E. coli, coliforms, enterococci) (Payment et al., 1985; Smeets et al., 2006). Membrane filtration technologies are also capable of removing 4 log to greater than 6 log of bacteria (Smeets et al., 2006). Disinfectants commonly used in the drinking water industry, such as chlorine, chloramine, chlorine dioxide, ozone, and ultraviolet (UV) light, are known to be effective against the enterococci group. Each of the above agents has demonstrated the ability to produce greater than a 4 log inactivation of enterococci in laboratory or pilot-scale experiments (Chang et al., 1985; Fujioka et al., 1986; Harris et al., 1987; Rice et al., 1993; Restaino et al., 1995; Wiedenmann et al., 1997; Grunert et al., 2018; Stange et al., 2019).
Scientific studies have provided some evidence of the enterococci group being more resistant to inactivation with chlorine, monochloramine, chlorine dioxide and UV light as compared to E. coli (Chang et al., 1985; Harris et al., 1987; Rice et al., 1993; Perez Recuerda et al., 1998; Tavakoli et al., 2005; Grunert et al., 2018; Léziart et al., 2019; Stange et al., 2019). However, the limited data makes it difficult to draw strong conclusions). Developments on this topic will continue to be monitored. Still, it is generally accepted that enterococci responses to disinfection are of the same order of magnitude as E. coli (Hijnen et al., 2011). Overall, the evidence shows that enterococci are much more sensitive to chlorination than the enteric protozoans Giardia and Cryptosporidium, and more sensitive to UV inactivation than certain enteric viruses (Smeets et al., 2006; Hijnen et al., 2011; Health Canada 2019a; 2019b). Therefore, water that is treated to meet the guidelines for enteric viruses and enteric protozoa should have an acceptable bacteriological quality, including achieving enterococci concentrations of none detectable per 100 mL of water leaving the treatment plant. Further information on inactivation of specific protozoan and viral pathogens can be found in the guideline technical documents on enteric protozoa and enteric viruses (Health Canada, 2019a; 2019b).
In distribution systems, a disinfectant residual is needed to protect against bacterial regrowth and serve as a sentinel for water quality changes. Regular monitoring of distribution system water quality (e.g., microbial indicators, disinfectant residual, turbidity, pH) and having operations and maintenance programs in place (water mains cleaning, cross-connection control, replacements and repairs) are important for ensuring drinking water is distributed to consumers with minimum loss of quality (Kirmeyer et al., 2001, 2014).
Surface water is not recommended as a residential-scale water supply unless it is properly filtered, disinfected and monitored for water quality. Well water supplies can also be contaminated and may require treatment. Various options are available for treating source waters to provide high-quality pathogen-free drinking water. These include systems that rely on chlorine, UV light or filtration. Health Canada does not recommend specific brands of residential-scale drinking water treatment devices, but it strongly recommends that consumers look for a mark or label indicating that the device has been certified by an accredited certification body as meeting the appropriate NSF International (NSF)/American National Standards Institute (ANSI) standard. These standards have been designed to safeguard drinking water by helping to ensure the safety of material and performance of products that come into contact with drinking water. Treatment devices should be inspected and serviced in accordance with the maintenance schedule and manufacturer’s recommendations.
B.5 International considerations
The European Union (EU) Drinking Water Directive has included enterococci (originally fecal streptococci) as a microbiological drinking water parameter since 1980 (1980; 1998). The current EU Drinking Water Directive outlines the legislative requirements for all its Member States (1998). Under the directive, enterococci are categorized as a parameter for audit monitoring in the distribution system. Audit parameters are tested less frequently than check (i.e., routine monitoring) parameters; they are intended to provide information as to whether or not their specific parametric values are being complied with. The EU standard for enterococci is a value of zero per 100mL (1998).
The Guidelines for Drinking Water Quality by the World Health Organization (WHO) (2017) contain fact sheets on numerous microbial indicators, including intestinal enterococci. The guidance from WHO specifies that the intestinal enterococci group can be used as an index of fecal pollution. The presence of the group provides evidence of recent fecal contamination, and detection of intestinal enterococci should lead to consideration of further action. No guideline values are specified.
The Australian Drinking Water Guidelines provide fact sheets on numerous microbial indicators, including intestinal enterococci, but no guideline values are specified. In practice, enterococci can be used to assess source water quality, the adequacy of treatment, post-treatment ingress into the distribution system and the delivery of safe drinking water at consumer taps (NHMRC and NRMMC, 2017).
The U.S. EPA Ground Water Rule (2006a) lists enterococci as one of three possible microbiological indicators of fecal contamination, alongside E. coli and coliphages, which can be specified by the states. Under the rule, untreated ground water systems having a total coliform-positive sample must collect at least one sample from each ground water source and test for one of the state-specified indicators (referred to as triggered source water monitoring). Should a triggered sample test positive for the fecal indicator, the system must notify state authorities and the public and take corrective actions.
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