Water withdrawal and consumption by sector indicator: data sources and methods, chapter 4

4. Methods

The Statistics Canada tables Water use in Canada by sector and Physical flow account for water use summarized results from the Industrial Water Survey (IWS), Agricultural Water Survey (AWS), Survey of Drinking Water Plants (SDWP), and Environment Canada's Municipal Water and Wastewater Survey (MWWS). Water withdrawal data for the thermal power generation, manufacturing, households, commercial and institutional, and oil and gas sectors were taken directly from these tables.

Water withdrawal estimates for the households sector prior to 2011 were based on water use by households served by municipal water supply systems from Environment Canada's Municipal Water Use Database (MUD). Estimates were also made for the portion of the population not served by municipal systems by multiplying the number of persons by a per capita water-use coefficient for self-supplied households.^{Footnote [1]} Recent estimates for the sector for 2011 and 2013 are based on the municipal water supply from SDWP. They are combined with an estimate from the drinking water producers of the proportion of this water supply that serves households. Water use by households not served by the municipal supply is estimated based on average household consumption figures.^{Footnote [2]}

Water withdrawal estimates for the mining sector were calculated by summing mine water estimates from Statistics Canada's IWS with mine water intake values. Mine water is water removed from mines through dewatering. The IWS reports mine water and water intake (withdrawal) separately.

Water withdrawal for the agriculture sector is calculated based on water volumes used for irrigation taken from the Statistics Canada's AWS. The amount of water used to water livestock and clean farm buildings is estimated using data from the Census of Agriculture.

For the households sector and the commercial and institutional sector, water consumption was assumed to be 10% of total water withdrawal based on consumption rates from Environment Canada's MWWS.^{Footnote [3]}

Water consumption values for the thermal power, manufacturing and mining sectors were taken from the appropriate IWS tables. The estimate of water consumption for the mining sector is calculated by subtracting mining discharge volumes from the withdrawal estimate.

Water consumption values for agriculture were calculated as the difference between the volume of water withdrawn from a river for irrigation and the volume measured as return flows back to the river. Consumption was calculated as 79.7% based on 20.3% of water being returned to the river system in 2013.^{Footnote [4]} The volume of water used for irrigation is managed to match crop water requirements; thus, water consumption by agriculture varies annually depending on the weather, with much less consumption during wet years.

For the oil and gas sector, consumption was estimated using the upper limit of an 80% to 95% range of the total water withdrawn by the oil sands industry being recycled and so not returned to groundwater and surface water sources.^{Footnote [5]}