Survey of Drinking Water Plants

Detailed information for 2005 to 2007





Record number:


The Survey of Drinking Water Plants is conducted to provide Canadians with national and regional information related to the production of drinking water.

Data release - October 27, 2009 (first in a series of releases. Please refer to left sidebar under the heading "The Daily")


The survey is a census of drinking water plants serving 300 or more people, and asks for information on volumes of water treated, type of treatment, financial aspects of the operation, as well as raw (source) water quality.

The survey results will produce a national portrait of treatment processes and costs, and source water quality across Canada, for facilities that range from ones with complex treatment processes to basic groundwater well supplies that provide minimal or no treatment. These data will be used to track the state of source water stocks and treatment on a regional basis and will also be used in the development of environmental accounts and indicators.

Reference period: Calendar year


  • Environment
  • Environmental quality

Data sources and methodology

Target population

The target population is composed of drinking water treatment plants that are licensed and regulated by provincial/territorial agencies and that draw and process source/raw water from the environment to produce treated/potable water for consumption, serving 300 or more people. The survey does not include information on the distribution of treated water.

Instrument design

The survey questionnaire was designed to collect data on treatment costs, processes used and both source (raw) and treated (finished) water quality. The questionnaire was developed in collaboration with subject matter experts at Health Canada and Provincial experts. A number of respondents were also consulted through individual meetings to ensure the information being asked was available and that the questionnaire could be filled out within a reasonable timeframe.

Environmental Accounts and Statistics Division, in consultation with Questionnaire Design Resource Centre, conducted testing of the questionnaires in July, September and October 2007 across Canada which included Atlantic Canada (5 locations), Québec (6 locations), Ontario (7 locations) and Western Canada (6 locations). Working group meetings were held with representatives of Environment Canada and Health Canada and final changes to the questionnaire where made based on the results of the field testing and the needs of the source water quality indicator being developed by Health Canada.


This survey is a census with a cross-sectional design.

Data are collected for all units of the target population; therefore, no sampling is done.

Survey frame
The target population is derived from a survey frame that was built in 2007 when Statistics Canada requested the inventories of drinking water plants held by the provinces and territories.

Excluding systems that supply water to communities with less than 300 people and other regulated systems that service schools, camp grounds, commercial establishments, provincial parks, etc., a survey frame of approximately 2,600 drinking water facilities serving communities of 300 or more people was compiled, the majority being publicly-owned (municipal) systems.

During collection and follow-up with non-respondents, approximately 400 drinking water facilities on the frame were identified as being out-of-scope (that is, the facilities served fewer than 300 people in 2007 or systems that only distributed water).

Data sources

Data collection for this reference period: 2008-06-19 to 2009-03-31

Responding to this survey is mandatory.

Data are collected directly from survey respondents.

Data were collected using mail out - mail back questionnaires.

Mail out occurred in June 2008 and respondents were asked to return the completed questionnaires within 60 days of receipt. The surveys were addressed to a contact person who was either responsible for, or had knowledge of, the drinking water facility being surveyed. A letter explaining the purpose of the survey, the requested return date and the legal requirements of response was included with the mail-out package.

Data were collected using one of two questionnaires: the printed version mailed to all respondents, or an electronic PDF form which allowed data to be entered and saved. The electronic PDF form, once completed, needed to be printed and mailed back. Telephone and fax follow-up were used to obtain data from respondents who returned incomplete questionnaires or who failed to respond.

View the Questionnaire(s) and reporting guide(s) .

Error detection

Many factors affect the accuracy of data produced in a survey. For example, respondents may have made errors in interpreting questions, answers may have been incorrectly entered on the questionnaires, and errors may have been introduced during the data capture or tabulation process. Every effort was made to reduce the occurrence of such errors in the survey.

Returned data are first entered and checked using the capture and edit software. This procedure verifies that all mandatory cells have been filled in, that certain values lie within acceptable ranges, that questionnaire flow patterns have been respected, and that totals equal the sum of their components. Collection officers evaluate the edit failures and concentrate follow-up efforts accordingly. Phone follow-ups are performed to verify information in cases where edit checks have failed.

Further data checking is performed by subject matter officers who review returned data that has been identified statistically as outliers and who compare returned data from 2005, 2006 and 2007 to determine if data differences between years are reasonable. In some instances, collection officers are asked to confirm responses with the respondents. Subject matter officers also research drinking water plants (annual reports, web sites, etc.) in an effort to verify information submitted by respondents.


Statistical imputation is used for records with incomplete questionnaire responses. Six methods of imputation are used for the Survey of Drinking Water Plants: deterministic imputation (only one possible value for the field to impute), imputation by linear regression, trend imputation, imputation by 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. The criteria for ratio and donor imputation are various combinations of water treatment type, source water type and geographical location (province, region, or Canada). No imputation is conducted on water quality variables.


In the estimation process, the response values are multiplied by a factor adjustment (weight) to account for plants in the population who could not be contacted or were unable to participate in the survey. No estimation is conducted on water quality variables.

Quality evaluation

This is the first time this survey has been conducted, therefore no historical data was available for comparison. In addition to analyzing individual responses for consistency within a questionnaire, both individual responses and weighted estimates of totals were compared to outside sources, where possible.

Disclosure control

Statistics Canada is prohibited by law from releasing any data that would divulge information obtained under the Statistics Act that relates to any identifiable person, business or organization without the prior knowledge or the consent in writing of that person, business or organization. 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.

Respondents have the option to sign the waiver attached to the Survey of Drinking Water Plants which grants permission to the Chief Statistician to authorize the release of the data specified by the waiver.

Revisions and seasonal adjustment

This methodology does not apply to this survey.

Data accuracy

Sampling error arises from the fact that the information obtained from a sample of the population is applied to the entire population. Since the Survey of Drinking Water Plants is a census, the sampling error is zero.

Data 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. Measures have been taken to minimize these errors.

Non-response errors result when plants refuse to answer, are unable to respond or are too late in reporting. Missing data items are imputed for partial non-responses (i.e. when mandatory questions are answered and some other questions are left unanswered).

The response rate for the survey was 54% in reference year 2005, 56% in reference year 2006 and 56% in reference year 2007. Overall, 58% of the population responded in one or more of the reference years 2005, 2006 and 2007. Note: There was low response to the survey from drinking water plants in Nunavut. Nunavut is not included in the response rate, nor is it included in any of the data tables.

Total non-response (i.e. when mandatory questions are left unanswered) is dealt with by adjusting the weights assigned to the responding units, such that one responding unit might also represent other non-responding units with similar characteristics (i.e. province, drainage region, source water type, size of population served). The error in the estimates due to total non-response is called total non-response error. The pattern of total non-response, the estimation method, the number of respondents and the variability associated with each measured variable determines the total non-response error. If the total non-respondents are assumed to be randomly "selected" from the population, then the respondents may be treated statistically as a random sample. Under this assumption, a possible measure of total non-response error is the coefficient of variation (CV). It represents the variability of the estimate as a proportion of the estimate. For this survey, CVs were calculated for the major variables and are indicated on the data tables. This information is available in the Statistics Canada publication entitled "Survey of Drinking Water Plants " (catalogue number 16-403-X), accessible through the 'Publications' link in the side bar menu at the upper left of this screen (scroll up to view).

A legend of the symbols used for the CV in our tables follows (standard table symbols are found in the link below):

A excellent data quality (coefficient of variation is 0.01% to 4.99%)
B very good data quality (coefficient of variation is 5.00% to 9.99%)
C good data quality (coefficient of variation is 10.00% to 14.99%)
D acceptable data quality (coefficient of variation is 15.00% to 24.99%)
E use with caution (coefficient of variation is 25.00% to 49.99%)
F too unreliable to be published (coefficient of variation greater than 49.99%)

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