Municipal Wastewater Systems in Canada (MWSC)

Detailed information for 2018-2020





Record number:


This statistical program is conducted to provide Canadians with national and regional information related to the volumes of wastewater (sewage) processed by municipal wastewater systems in Canada.

Data release - May 11, 2023


This statistical activity is a census of municipal wastewater systems in Canada with daily flows of 100m³/day or more. The results produce a national portrait of discharge volumes and treatment processes across Canada. These data will be used in the development of environmental accounts and indicators.

Reference period: Calendar year


  • Environment
  • Environmental quality
  • Pollution and waste

Data sources and methodology

Target population

The target population is composed of municipal wastewater systems in Canada with a daily flow of 100m³/day or more. Excluding systems that service first nations reserves, government institutions, commercial and industrial establishments, provincial parks, etc., a list of approximately 2,000 wastewater (sewage) systems serving communities with a daily flow of 100m³/day or more was created, the majority being public (municipal) systems.

Of the 2,000 wastewater (sewage) systems, approximately 700 have combined sewers with overflow structures. Combined sewer systems convey both sewage and storm water to wastewater treatment plants. Many of these systems have multiple overflow structures that may discharge untreated sewage mixed with storm water into receiving waters when full capacity has been reached during intense rainfall events.

The target population is derived from owners of wastewater (sewage) systems that report under the federal Wastewater Systems Effluent Regulations (WSER). Other systems not reporting under the WSER, such as those in northern regions under an equivalency agreement, are also added to the frame.

Where necessary, inventories of wastewater systems held by the Provinces and Territories are used to update the frame.

Instrument design

This methodology type does not apply to this statistical program.


This statistical activity is a census. Data are collected for all units of the target population; therefore, no sampling is done.

Data sources

The data are derived from administrative records collected by Environment Canada and Climate Change (ECCC) via the Effluent Regulatory Reporting Information System (ERRIS), as required by the WSER. WSER records of wastewater (sewage) systems and the communities they service are linked to census population data. Linkages of some records to on-line information, such as municipal reports and provincial reports, are also made to facilitate the imputation and estimation for missing records not reported to ECCC. The data are then processed by Statistics Canada to produce estimates of the target population.

Error detection

Collected data are processed using MS-Access, Excel and SAS programs for review and editing. This procedure verifies that all core cells have been filled in, that certain values lie within acceptable ranges and that totals equal the sum of their components. Further data checking is performed by subject matter officers who review data that have been identified statistically as outliers. Comparison with data from previous years is carried out to determine if the differences between years are reasonable. Subject matter officers also research wastewater (sewage) systems (annual reports, web sites, etc.) in an effort to verify information.


Five methods of imputation are used for this statistical activity:
- deterministic imputation (only one possible value for the field to impute),
- imputation by historical value (use of data from previous cycles),
- imputation by current ratio,
- donor imputation (using a "nearest neighbour" approach to find a valid record that is most similar to the record requiring imputation in terms of treated water volume and other characteristics), and
- manual imputation.

All of these imputation methods (except manual imputation) are implemented using the BANFF software, version 2.07. The ratio and donor imputation methods are executed with various combinations of wastewater treatment type and geographical location (province, region, or Canada).

These methods of imputation are used to impute partial and total non-response.


Because this statistical activity is a census, each unit has a design weight of 1. Since it is a census, and all the total non-response units are is imputed, the final weights are equal to the design weights.

Totals of monthly and annual volumes are produced by the Generalized Estimation System (GES).

Quality evaluation

Micro data evaluation and error detection are important processes used to ensure good quality data. However, the final estimates obtained through the use of this micro data must also be evaluated in order to ensure accuracy. The quality of the estimates produced from a statistical activity can be assessed through comparison to the trends obtained from other data sources and/or through a historical comparison to data obtained previously through the same statistical activity. Estimates for the municipal wastewater systems in Canada are compared with the estimates from previous reference periods. This historical comparison is made to ensure that the estimates are coherent.

Disclosure control

Statistics Canada is prohibited by law from releasing any information it collects which could identify any person, business, or organization, unless consent has been given by the respondent or as permitted by the Statistics Act. Various confidentiality rules are applied to all data that are released or published to prevent the publication or disclosure of any information deemed confidential. If necessary, data are suppressed to prevent direct or residual disclosure of identifiable data.

A Discretionary Disclosure Order (DDO) pursuant to paragraph 17(2)(a) of the Statistics Act was obtained to allow increased disclosure of aggregate information. The DDO permits the release of wastewater system data, allowing the dissemination of a complete national profile of information related to the processing of wastewater (sewage) by public utilities.

Revisions and seasonal adjustment

Revisions are made for the previous statistical activity reference period, with the initial release of the current data, as required. The purpose is to address any significant issues with the data that are found between statistical activity cycles. The actual period of revision depends on the nature of the issue. For the most current data please refer to tables 38100099, 38100100, 38100119, 38100124, 38100125. The data are not seasonally adjusted.

Data accuracy

Sampling error can arise when the information obtained from a sample of a population is used to derive an estimate for the entire population. Since the statistical activity of Municipal Wastewater Systems in Canada is a census, sampling error is null.

Response error may be due to questionnaire design, the characteristics of a question, inability or unwillingness of the respondent to provide correct information, misinterpretation of the questions or conceptual problems. These errors are controlled through careful questionnaire design and testing and the use of simple concepts and consistency checks.

Processing errors may occur at various stages of processing such as data entry, editing and tabulation. All efforts are undertaken to minimize non-sampling errors through extensive edits, quality control steps and data analysis, but some of these errors are outside the control of Statistics Canada.

Non-response errors result when respondents refuse to answer, are unable to respond or are too late in reporting. Missing data items are imputed for partial and total non-responses.

Total non-response is defined as units that do not report values for any of the mandatory variables in this statistical activity. In order to limit total non-response (to minimize non-response bias), cases where all mandatory variables are blank are examined manually and every effort is made to manually impute values for them.

Since this statistical activity is a census and all non-response has been imputed, the sampling error is zero (0) which give a CV of zero (0). To take into account that imputation has occurred, both the sampling error (which is 0 for every estimate) and the non-response rate are combined into one quality rating code for each estimate. This code uses letters that range from A to E where A means the estimate is of excellent quality and E means it is to be used with caution.

A: excellent data quality (CV is 0 and non-response rate is 10% or lower)
B: very good data quality (CV is 0 and non-response rate is 10.01% to 33%)
C: good data quality (CV is 0 and non-response rate is 33.01% to 60%)
E: use with caution (CV is 0 and non-response rate is greater than 60%)

Weighted total annual effluent volume response rates:
For 2013, it is 94%.
For 2014, it is 94%.
For 2015, it is 93%.
For 2016, it is 93%.
For 2017, it is 93%.
For 2018, it is 97%.
For 2019, it is 97%.
For 2020, it is 97%

Weighted total combined sewer overflow volume response rates:
For 2013, it is 92%.
For 2014, it is 82%.
For 2015, it is 85%.
For 2016, it is 86%.
For 2017, it is 83%.
*For 2018, it is 99%.
*For 2019, it is 100%.
*For 2020, it is 100%.
* As of 2018, no combined sewer overflow volumes from Quebec municipalities are available.

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