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Document ID ca-guqmradw-2018-03-09 Title Guidance on the Use of Quantitative Microbial Risk Assessment in Drinking Water URL https://www.canada.ca/en/health-canada/programs/consultations-guidance-quantitative-microbial-risk-assessment-drinking-water/document.html Jurisdiction /ca Subdomain(s) Drinking water, Water treatment Language en Status completed Analyzed at 2026-03-17 12:49:40.910375+00:00 Relevance Technical guidance on microbial risk assessment for drinking water treatment.

32 Qualitative 53 Quantitative 0 Definitions

Q Qualitative Requirements (32)

Req ID	Category	Intent	Legal Status	Name	Subdomain(s)	Context	Conditions	Confidence
#Q001	administrative	operational	recommended	Site-specific Risk Assessment Approach	drinking water	The type of risk assessment needed for any given water system should be determined on a site-specific basis.		high
#Q002	administrative	operational	recommended	Determination of Assessment Scope	drinking water	The first step that should be undertaken when starting a risk assessment is to determine the scope of the assessment.	When starting a risk assessment	high
#Q003	administrative	operational	recommended	Quantitation in Risk Assessments	drinking water	It is recommended that all risk assessments provide some level of quantitation to help guide risk managers when prioritizing tasks (WHO, 2016).		high
#Q004	administrative	operational	recommended	Sensitivity Analysis Inclusion	drinking water	Sensitivity analyses, which include variability and uncertainty evaluations, should be incorporated in risk assessment when possible.	When possible	high
#Q005	reporting	reporting	mandatory	Documentation of Risk Assessment Assumptions	drinking water	In order to properly interpret risk estimates, the limitations and assumptions associated with a risk assessment need to be well documented and understood.		high
#Q006	administrative	operational	recommended	Use of Additional Pathogen Information	drinking water	Due to the limitations associated with pathogen data, they should be used in conjunction with all the other information that is available for the system when conducting a risk assessment.	When conducting a risk assessment	high
#Q007	administrative	operational	recommended	Gathering Treatment Barrier Information	drinking water	Utilities should make every effort to gather as much information as they can on their specific system using whatever data they have available, such as design parameters or performance assessments.		high
#Q008	reporting	reporting	mandatory	Recording Treatment Assumptions	drinking water	It is important to consider what level of detail is needed for the treatment system and then record all assumptions that are being made.		high
#Q009	administrative	operational	recommended	Use of Multiple Assessment Scenarios	drinking water	To capture the range of risk estimates that are possible in a water system, users should run multiple scenarios ranging from expected conditions to situations that represent conservative estimates.		high
#Q010	reporting	reporting	mandatory	Documentation of Model Inputs	drinking water	Because of this flexibility, it is important to fully document the information that is being inputted into the model, including how representative this information is believed to be for the system, to accurately interpret the risk estimates that are obtained.		high
#Q011	monitoring	health	recommended	Implementation of Source Water Monitoring	drinking water	Where feasible, water providers are encouraged to implement a source water monitoring program that includes monitoring for reference pathogens, to provide site-specific information on the microbiological quality of the water.	Where feasible	high
#Q012	reporting	reporting	recommended	Sample Identification Classification	drinking water	Collected samples should be identified as either baseline (routine) samples or as event (incident) samples.		high
#Q013	reporting	reporting	recommended	Documentation of Event Sample Conditions	drinking water	Information that defines the sample as an event sample should be included so that the conditions that constituted the event are clear.	When sample is an event sample	high
#Q014	administrative	operational	recommended	Inclusion of Limit of Detection Considerations	drinking water	When determining mean and standard deviations, risk assessors should consider how method recovery will be incorporated, and identify how data that is below the limit of detection (LOD) will be included in the calculation.	When determining mean and standard deviations	high
#Q015	monitoring	operational	recommended	Assessment of Method Recovery	drinking water	where possible, it is recommended that the recovery of these methods be assessed.	Where possible	high
#Q016	monitoring	health	recommended	Assessment of Viability and Infectivity	drinking water	Where possible, assessing the viability and infectivity of the reference pathogens is recommended.	Where possible	high
#Q017	prohibition	reporting	mandatory	Prohibition of Using Zero for Values Below LOD	drinking water	Samples below the LOD should not be included as zeros in the calculation of mean and standard deviation; although no organisms were recovered, this does not mean that the source water has a concentration of zero.	When calculating mean and standard deviation	high
#Q018	reporting	reporting	mandatory	External Recording of Input Parameters	drinking water	The input parameters and the corresponding results calculated by the model will need to be recorded elsewhere as the model does not store the data for the user.		high
#Q019	operational	treatment	recommended	Acquisition of Disinfection Process Data	drinking water	It is important to enter data for each of the parameters that describe the disinfection process. If this information is not available for the specific treatment system, operations should be carefully examined in an effort to acquire these data.	If information is not available for the specific treatment system	high
#Q020	monitoring	operational	recommended	Monitoring Program Design Goal	drinking water	The goal of a monitoring program should be to sample for the organisms of interest to an extent and at a frequency that capture the most important sources of variation in microbiological source water quality.		high
#Q021	administrative	health	mandatory	Annual Health Risk Target Level	drinking water	When using an annual target, it is important that it be set at a level that does not allow the variability in water quality to exceed what would be tolerable over a short term event.	When using an annual target	high
#Q022	administrative	operational	mandatory	Fallback for Missing Recovery Efficiency	drinking water	In the absence of recovery efficiency information, recoveries will either need to be based on other published literature or be assumed to be 100% (Schijven, 2011).	In the absence of recovery efficiency information	high
#Q023	administrative	operational	mandatory	Unit Standard for Model Inputs	drinking water	All pathogen concentrations, including E. coli, are entered in number of organisms per 100 L of water.		high
#Q024	administrative	operational	mandatory	Treatment Selection for Conventional Systems	drinking water	for conventional treatment, both coagulation/flocculation/sedimentation and granular filtration (with coagulation/sedimentation) need to be selected to represent full conventional treatment.	for conventional treatment	high
#Q025	administrative	operational	mandatory	Evaluation of Data Collection Costs	drinking water	if the questions that need to be answered by the risk assessment require an in-depth probabilistic assessment, then the cost of collecting the data required for the analysis needs to be weighed against the cost of making resource decisions based on assumptions.	if the questions that need to be answered by the risk assessment require an in-depth probabilistic assessment	high
#Q026	operational	operational	mandatory	Pathogenic E. coli Data Adjustment	drinking water	If a drinking water system has E. coli O157:H7 data and is entering this directly, the percentage of 3.4% will need to be changed to 100%.	If a drinking water system has E. coli O157:H7 data and is entering this directly	high
#Q027	administrative	operational	recommended	Consideration of Available Treatment Data	drinking water	Treatment barrier performance decisions should also consider the data that is routinely available, such as general source water quality data and operational data from the treatment plant.		high
#Q028	administrative	reporting	mandatory	Factors for Interpreting Risk Estimates	drinking water	When interpreting risk estimates, there are numerous factors that need to be considered. This includes the assumptions that were made, how they impact the risk estimates, and to what degree the variability and uncertainty has been captured during the assessment (including noting data gaps and sampling biases).	When interpreting risk estimates	high
#Q029	administrative	operational	recommended	Basis for Expert Judgment	drinking water	Expert judgement should be based on literature values from studies of similar types of water sources, if available, and take into consideration other site-specific information such as data from faecal indicators.	When using expert judgement for missing pathogen data	high
#Q030	operational	treatment	mandatory	Mandatory Disinfection Input Parameters	drinking water	To calculate the log inactivation for the chemical disinfectants (free chlorine, chloramines, ozone and chlorine dioxide), 6 parameters must be entered to describe the disinfection process (see Figure B3): contact time (min), baffle factor (T10/T), initial disinfectant concentration (mg/L), disinfectant decay factor (min-1), pH, and temperature (°C).	When calculating log inactivation for chemical disinfectants in the model	high
#Q031	administrative	unknown	guidance	Model Dose Limitation	drinking water	this model cannot be used to examine scenarios where the average ingested dose is greater than [100 organisms].	When using the HC QMRA model	high
#Q032	administrative	reporting	recommended	Public Consultation Privacy Statement	other	Authors who do not want their name and affiliation shared with their CDW member should provide a statement to this effect along with their comments.	During the public consultation period	high

P Quantitative Requirements (53)

Req ID	Category	Intent	Legal Status	Name	Subdomain(s)	Limit Type	Limit Value	Context	Conditions	Confidence
#P001	microbiological	health	guideline	Annual target risk	drinking water	treatment_goal	1 × 10-6 DALYs per person per year	The Guidelines for Canadian Drinking Water Quality use an annual target risk of 1 × 10-6 DALYs per person per year.		high
#P002	unknown	health	guidance	Average water consumption per day	drinking water	unknown	1.0 L	The model default for average water consumption per day (Water ConsumptionDay) is 1.0 L of unboiled tap water.	Assumed for model default, can be modified for specific populations	high
#P003	microbiological	health	guidance	Pathogenic E. coli default percentage	drinking water	requirement	3.4 %	The Health Canada model estimates the concentration of pathogenic E. coli, using the total E. coli data from source water(s), by assuming a default value of 3.4% of the total E. coli detected is a pathogenic strain.	Default assumption used to calculate pathogenic E. coli from total E. coli monitoring data	high
#P004	operational	operational	guidance	Model discrete dose upper limit	drinking water	requirement	100 organisms	In an effort to reduce model running times, the limit of 100 organisms was applied as a compromise... this model cannot be used to examine scenarios where the average ingested dose is greater than this value.	Technical constraint of the HC QMRA model analysis range for probability calculations	high
#P005	unknown	health	guidance	Combined life expectancy for DALY calculation	drinking water	requirement	80.88 years	The model uses the combined life expectancy (i.e. the average of male and female life expectancies - 80.88 years), as the reference pathogens do not have gender specific health outcomes.	Used as the reference value for calculating Life-Years-Lost (LYL) within the DALY metric	high
#P006	microbiological	health	guidance	Probability of illness given infection (Cryptosporidium)	drinking water	requirement	0.70 decimal fraction	The probability of illness given infection (Pill/inf) varies with each reference pathogen. The values used by the model for Pill/inf are based on the published literature...		high
#P007	microbiological	health	guidance	Probability of illness given infection (Giardia)	drinking water	requirement	0.40 decimal fraction	The values used by the model for Pill/inf are based on the published literature and are given in Table B2. Giardia is 0.40.		high
#P008	microbiological	health	guidance	Probability of illness given infection (Rotavirus)	drinking water	requirement	0.88 decimal fraction	The values used by the model for Pill/inf are based on the published literature and are given in Table B2. Rotavirus is 0.88.		high
#P009	unknown	health	guidance	Weighted median age for Canadian population	drinking water	requirement	38.98 years	For Cryptosporidium, Giardia, rotavirus, and E.coli O157, the weighted median age (38.98 years) is used as the age at death.	Used for calculating LYL when fatality rates are assumed not to differ between age categories.	high
#P010	unknown	health	guidance	Median age of eldest population category	drinking water	requirement	72.94 years	For Campylobacter, death primarily occurs in the elderly population. Therefore, the age at death is assumed to be the median age of the eldest population category (72.94 years).	Specific age at death assumption for Campylobacter fatality calculations.	high
#P011	microbiological	health	guidance	Outcome fraction for death (Cryptosporidium and Giardia)	drinking water	requirement	1 in 100,000 cases	The outcome fractions for death are assumed to be 1 in 100,000 for Cryptosporidium and Giardia.		high
#P012	microbiological	health	guidance	Outcome fraction for death (Rotavirus and Campylobacter)	drinking water	requirement	1 in 10,000 cases	Rotavirus and Campylobacter are assumed to have a case fatality ratio of 1 in 10,000.		high
#P013	microbiological	health	guidance	Outcome fraction for death (E. coli O157:H7)	drinking water	requirement	1 in 4,000 cases	For E.coli O157:H7, the risk of death is higher, at 1 in 4,000 (Havelaar and Melse, 2003).		high
#P014	operational	operational	guidance	Disinfectant decay factor typical range	drinking water	OG	0.001 to 0.2 min-1	In general, decay factors tend to fall in the range of 0.001 to 0.2 min-1 depending on the disinfectant being applied.	Typical operational values for disinfectants applied in the N-CSTR approach.	high
#P015	microbiological	health	guidance	Dose-response constant (Cryptosporidium)	drinking water	requirement	0.018 r	Constant derived from dose-response studies for the exponential model.		high
#P016	microbiological	health	guidance	Dose-response constant (Giardia)	drinking water	requirement	0.01982 r	Constant derived from dose-response studies for the exponential model.		high
#P017	design	treatment	guidance	Typical baffle factor range	drinking water	OG	0.3 to 0.7 ratio (T10/T)	Studies investigating numerous contact chamber sizes and configurations reported T10/T ratios between 0.3 and 0.7.	Based on geometry of the contact chamber	high
#P018	unknown	health	guidance	Mild diarrhea severity weight	drinking water	requirement	0.067 weight	Severity weight assigned to the 'Mild diarrhea' outcome fraction for DALY calculations.		high
#P019	unknown	health	guidance	Duration of mild diarrhea (Crypto/Giardia/Rotavirus)	drinking water	requirement	7 days	Standardized duration of illness in years (0.01918) used for Cryptosporidium, Giardia, and Rotavirus.		high
#P020	microbiological	health	guidance	Dose-response parameters (Rotavirus)	drinking water	requirement	alpha = 0.265, beta = 0.4415 constant	Parameters for the beta-Poisson model used for rotavirus.		high
#P021	microbiological	health	guidance	Dose-response parameters (E. coli O157:H7)	drinking water	requirement	alpha = 0.0571, beta = 2.2183 constant	Parameters for the beta-Poisson model used for E. coli O157:H7.		high
#P022	microbiological	health	guidance	Dose-response parameters (Campylobacter)	drinking water	requirement	alpha = 0.145, beta = 7.59 constant	Parameters for the beta-Poisson model used for Campylobacter.		high
#P023	microbiological	health	guidance	Bloody diarrhea severity weight	drinking water	requirement	0.39 weighting factor	Severity weight for bloody diarrhea used in YLD calculations.		high
#P024	microbiological	health	guidance	Hemolytic uremic syndrome (HUS) severity weight	drinking water	requirement	0.93 weighting factor	Severity weight for HUS used in YLD calculations.		high
#P025	microbiological	health	guidance	End-stage renal disease (ESRD) severity weight	drinking water	requirement	0.95 weighting factor	Severity weight for ESRD used in YLD calculations.		high
#P026	microbiological	health	guidance	Probability of illness given infection (E. coli O157:H7)	drinking water	requirement	1.0 decimal fraction	The dose-response model estimates the probability of illness directly, so Pill/inf is 1.0.		high
#P027	microbiological	health	guidance	Probability of illness given infection (Campylobacter)	drinking water	requirement	1.0 decimal fraction	Current studies do not provide a consistent value; 1.0 is used as a conservative estimate.		high
#P028	microbiological	health	guidance	Duration of end-stage renal disease (ESRD)	drinking water	requirement	9.35 years	Chronic duration used for ESRD outcomes in DALY calculations.		high
#P029	microbiological	health	guidance	Duration of hemolytic uremic syndrome (HUS)	drinking water	requirement	0.0575 years	Assumed duration for HUS outcomes (approximately 21 days).		high
#P030	operational	operational	guidance	Model integration slices	drinking water	requirement	500 slices	The model divides the log-normal distribution curve into approximately 500 integration slices.		high
#P031	operational	operational	guidance	N-CSTR integration slices	drinking water	requirement	1000 slices	The distribution is divided into 1000 integration slices within the N-CSTR approach.		high
#P032	microbiological	health	guidance	Hemolytic uremic syndrome (HUS) outcome fraction	drinking water	requirement	0.01 decimal fraction	Outcome fraction for HUS attributed to E. coli O157 used in YLD calculations.		high
#P033	microbiological	health	guidance	End-stage renal disease (ESRD) outcome fraction	drinking water	requirement	0.00118 decimal fraction	Outcome fraction for ESRD attributed to E. coli O157 used in YLD calculations.		high
#P034	microbiological	health	guidance	Reactive arthritis outcome fraction	drinking water	requirement	0.023 decimal fraction	Outcome fraction for reactive arthritis attributed to Campylobacter used in YLD calculations.		high
#P035	microbiological	health	guidance	Guillain-Barré syndrome (GBS) outcome fraction	drinking water	requirement	0.0002 decimal fraction	Outcome fraction for GBS (clinical and residual) attributed to Campylobacter used in YLD calculations.		high
#P036	microbiological	health	guidance	Reactive arthritis duration	drinking water	requirement	0.115 years	Duration of illness used for reactive arthritis (approximately 42 days).		high
#P037	microbiological	health	guidance	Clinical GBS DALY impact	drinking water	requirement	0.29 DALYs per case	Expressed in DALYs per case of illness as derived from a complex combination of disease stages.		high
#P038	microbiological	health	guidance	Residual GBS DALY impact	drinking water	requirement	5.8 DALYs per case	Expressed in DALYs per case of illness for residual symptoms of GBS.		high
#P039	microbiological	health	guidance	Serious (bloody) diarrhea outcome fraction (E. coli O157)	drinking water	requirement	0.47 decimal fraction	Outcome fraction for bloody diarrhea attributed to E. coli O157.		high
#P040	microbiological	health	guidance	Serious (bloody) diarrhea duration (Campylobacter)	drinking water	requirement	0.023 years	Duration of serious diarrhea (approximately 8.4 days).		high
#P041	microbiological	health	guidance	Mild diarrhea outcome fraction (Campylobacter)	drinking water	requirement	0.5 decimal fraction	Outcome fraction for mild diarrhea attributed to Campylobacter.		high
#P042	microbiological	health	guidance	Mild diarrhea outcome fraction (E. coli O157)	drinking water	requirement	0.53 decimal fraction	Outcome fraction for mild diarrhea attributed to E. coli O157.		high
#P043	operational	reporting	guidance	Recommended average organisms per sample	drinking water	requirement	>= 10 organisms	Ideally, to get the best estimates of source water pathogen concentrations, the volume of sample analysed would be sufficient to have an average of at least 10 organisms in the sample.	Target for sample volume and analysis for reliable concentration estimates	high
#P044	microbiological	health	guidance	Outcome fraction for death (GBS)	drinking water	requirement	4.6E-06 decimal fraction	Death (GBS) outcome fraction attributed to Campylobacter (1 in 217,000).		high
#P045	microbiological	health	guidance	Outcome fraction for mild diarrhea (Rotavirus)	drinking water	requirement	0.5 decimal fraction	Fraction of Rotavirus infections resulting in mild diarrhea used in YLD calculations.		high
#P046	microbiological	health	guidance	Outcome fraction for bloody diarrhea (Rotavirus)	drinking water	requirement	0.5 decimal fraction	Fraction of Rotavirus infections resulting in bloody diarrhea used in YLD calculations.		high
#P047	microbiological	health	guidance	Outcome fraction for bloody diarrhea (Campylobacter)	drinking water	requirement	0.5 decimal fraction	Fraction of Campylobacter infections resulting in bloody diarrhea.		high
#P048	microbiological	health	guidance	Outcome fraction for mild diarrhea (Cryptosporidium and Giardia)	drinking water	requirement	0.99999 decimal fraction	Fraction of infections resulting in mild diarrhea for Cryptosporidium and Giardia.		high
#P049	microbiological	health	guidance	Duration of mild diarrhea (Campylobacter)	drinking water	requirement	0.01397 years	Standardized duration of mild diarrhea (5.1 days).		high
#P050	microbiological	health	guidance	Duration of mild diarrhea (E. coli O157)	drinking water	requirement	0.00932 years	Standardized duration of mild diarrhea (3.4 days).		high
#P051	microbiological	health	guidance	Duration of serious (bloody) diarrhea (Rotavirus)	drinking water	requirement	0.01918 years	Standardized duration of serious (bloody) diarrhea (7 days).		high
#P052	microbiological	health	guidance	Duration of serious (bloody) diarrhea (E. coli O157)	drinking water	requirement	0.01534 years	Standardized duration of serious (bloody) diarrhea (5.6 days).		high
#P053	unknown	health	guidance	Severity weight for loss of life	drinking water	requirement	1.0 weighting factor	In all instances, a severity weight of 1.0 is assigned for loss of life.	Applied to Life-Years-Lost (LYL) calculations for all reference pathogens	high

D Definitions (0)

No definitions.