Municipal wastewater treatment indicator: data sources and methods, chapter 3

3. Data

3.1 Data source

Data for 1983 to 1999 come from Environment Canada's Municipal Water Use and Pricing (MUD) surveys. In 2001, the survey was revised to become the Municipal Water and Wastewater Survey (MWWS). Data for 2004 to 2009 are taken from the MWWS. Survey results are available on the Municipal Water and Wastewater Survey's Data and Publications website.

3.2 Spatial coverage

Prior to 2001, the MUD survey was only sent to municipalities across Canada with populations greater than 1000. Since 2001, the survey has been sent to all municipalities with a population greater than 1000 and a sample of over 600 municipalities with fewer than 1000 residents. Municipalities on federal lands and First Nations communities are excluded from the MUD surveys and the MWWS.

3.3 Temporal coverage

The MWWS and its predecessor, the MUD survey, have been conducted every two to three years since 1983. The MUD survey was reformatted following the 1999 survey and the first MWWS was conducted in 2001. The 2001 MWWS has been excluded from the CESI indicator due to the low response rate to questions about sewage treatment levels.

3.4 Data completeness

Prior to 2001 the MUD survey collected information only from Canadian municipalities with a population greater than 1000. In 2001 the survey was expanded to include Canadian municipalities with populations less than 1000. In 2004 and 2006, the MWWS sampled 616 and 630 such municipalities, respectively. In 2009, the survey was expanded to include 1000 municipalities with fewer than 1000 residents. Overall, data remain comparable among surveys, because small municipalities have little effect on aggregate statistics due to population weighting.^{Footnote [1]} For more information on changes to the survey sample and methodology, see Environment Canada's Municipal Water Use Reports.

Survey response rates vary by survey year and question. In the 2009 MWWS, residential sewage disposal information was available for a responding population^{Footnote [2]} of 28 122 846 Canadians and wastewater treatment information was available for a responding population of 23 618 481 Canadians served by municipal sewers.^{Footnote [3]} Given the survey's response rate of approximately 70% of the Canadian population, it is assumed for the purposes of this indicator to be representative of the entire Canadian population.

3.5 Data timeliness

The MWWS is conducted every two to three years with data released approximately two years after the calendar year to which the collected data apply.