Survey of Drinking Water Plants

Detailed information for 2011

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 - May 29, 2013

• Questionnaire(s) and reporting guide(s)
• Description
• Data sources and methodology
• Data accuracy

Description

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

Collection period: January through May of the year after the reference period

Subjects

• 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 (excluding First Nations communities) and that draw and process source/raw water from the environment to produce treated/potable water for consumption, serving 300 or more people.

The observed population comes from a frame created in 2007. At that time, Statistics Canada requested the inventories of drinking water plants held by the provinces and territories. It excludes systems that supply water to communities with less than 300 people and other regulated systems that service schools, campgrounds, commercial establishments, provincial parks, etc. This frame is kept up to date using responses from previous survey cycles and through contact with potential respondents prior to mail out of each new cycle.

Instrument design

The survey questionnaire was designed to collect data on treatment costs, processes used and source (raw) 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 questionnaire 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 were made based on the results of the field testing. The revised 2011 questionnaire was tested in both official languages in the fall of 2010 at 9 locations (5 in Ontario and 4 in Québec).

Sampling

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 built from inventories of drinking water plants held by the Provinces and Territories. The frame is kept up to date using responses from previous survey cycles and through contact with potential respondents prior to mail out of each new cycle.

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 2,100 drinking water facilities serving communities of 300 or more people was compiled, the majority being public (municipal) systems.

During data collection for the 2011 reference year, approximately 100 drinking water facilities on the frame were identified as being out-of-scope because they served fewer than 300 people in 2011 or were systems that only distributed potable water. Approximately 25 new water facilities were added to the frame for 2011.

Data sources

Data collection for this reference period: 2012-01-01 to 2012-05-31

Responding to this survey is mandatory.

Data are collected directly from survey respondents.

Respondents are contacted to confirm contact information prior to the survey being sent. The questionnaires are mailed out and respondents are asked to return the completed forms within sixty days of receipt. The surveys are addressed to a contact person who is either responsible for, or has knowledge of, the drinking water plant being surveyed. A letter explaining the purpose of the survey, the requested return date and the legal requirement to respond was included with the mail-out package. Telephone and fax follow-up are used to obtain data from respondents who returned incomplete questionnaires or who failed to respond. Returned questionnaires are scanned using an imaging system that captures the data for transfer into a database. Some data are manually keyed in. A capture and edit software is applied to run edit checks on the data, which serve to identify real or potential response errors.

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

Error detection

Returned data are first entered and checked using the capture and edit software. This procedure verifies that all core 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 fail.

Further data checking is performed by subject matter officers who review returned 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. 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.

Imputation

Seven 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)
- imputation by historical value (use of data from previous cycles) 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). All of these methods are implemented using the BANFF software, version 2.04. No imputation is conducted on water quality variables.

The imputation rate for the 2011 Survey of Drinking Water Plants (number of affected cells) was approximately 5%.

Estimation

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.

Disclosure control

Statistics Canada is prohibited by law from releasing any information it collects that 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.

In order to prevent any data disclosure, confidentiality analysis is done using the Statistics Canada Generalized Disclosure Control System (G-Confid). G-Confid is used for primary suppression (direct disclosure) as well as for secondary suppression (residual disclosure). Direct disclosure occurs when the value in a tabulation cell is composed of or dominated by few enterprises while residual disclosure occurs when confidential information can be derived indirectly by piecing together information from different sources or data series.

Revisions and seasonal adjustment

Revisions are made for the previous survey reference period, with the initial release of the current data, as required. The purpose is to address any significant issues with the data that were found between survey cycles. The actual period of revision depends on the nature of the issue. For the most current data please refer to CANSIM tables 153-0105 to 153-0108. 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 Survey of Drinking Water Plants is a census, sampling error is zero.

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 non-responses.

Total non-response is dealt with by adjusting the weights assigned to units that did respond, 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 pattern of total non-response, the estimation method, the number of respondents and the variability associated with each measured variable determines total non-response error. If non-respondents are assumed to be randomly "selected" from the population, then responding units may be treated statistically as a random sample. Under this assumption, a measure of total non-response error is the coefficient of variation (CV). It represents the ratio of the standard error of a survey to the estimate itself. Thus, although the survey is a census, getting a nonzero CV is possible. For this survey, CVs are 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).

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% - data are suppressed for the purpose of publication and made available only upon user request)

The 95% confidence interval associated with an estimate (assuming a normal distribution) is given by:
Estimate ± 1.96 * (CV in %) * Estimate/100.

The response rate for the survey was 87% in reference year 2011.

• Additional documentation