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Section 3: The demand for water in Canada

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Water is implicated in all facets of human life: in the home, at work and at play. Some demands make use of water without removing it from the natural environment, while other demands require water to be extracted. Commercial fishing, shipping and recreational boating are examples of activities that are carried out in-stream. Household and most industrial activities, however, rely on water that is withdrawn from the environment. Measuring key socioeconomic uses of water provides information to support water management.

Some of the water that is withdrawn is used directly from the source, while other water is treated prior to its use. Treatment, which is done to improve water quality, may be done on-site by the user, or at a centralized facility. For example, treatment to make water suitable for paper manufacturing is typically done on-site, while in 2007 85% of the population of Canada received water that had been centrally treated and then distributed to households. 1 , 2 

Water use

In 2005, an estimated 42 km3 of water were withdrawn from the environment and used in household and economic activities in Canada (Table 3.1). About 14% of this water flowed through the public utility water system, and about 86% was extracted from the environment directly by the end user. About 10.5% of the water extracted directly from the environment was not freshwater (either brackish or salt-water), the bulk of which was used by the Thermal-electric power generation sector. 3 

More than 90% of the water that was withdrawn went to support economic activity, and about 9% was used directly by the residential sector. The residential sector used 56% of the water that was supplied by the public utility water system. The sector that used the most water overall, by a considerable margin, was Thermal-electric power generation (Table 3.1).

Water use by sector

Thermal-electric power generation

The Thermal-electric power generation sector, which is composed of nuclear and fossil fuel powered generating stations, withdrew the most freshwater in Canada in 2005. These generating stations draw large quantities of water, usually from surface water bodies, to aid in the cooling processes required for electricity generation. The use of water for cooling results in evaporation, accounting for much of the water consumed by this sector. Thermal-electric power generation used 66% (27.8 km3) of a total of 42 km3 of freshwater withdrawn in 2005 (Table 3.1). This sector recirculates a considerable portion of the water it withdraws. In 2005 the volume of water recirculated was about 15% of the total water that was withdrawn from the environment by this sector. 3 

Manufacturing industries

Manufacturing industries use water in numerous production activities, such as processing, cleaning and cooling. Water can also be added to the content of final products. In 2005, the manufacturing sector used the second largest amount of water, accounting for 14% (5.7 km3) of total water withdrawals (Table 3.1). Public utilities provided 10.8% of this water in 2005 and 13.2% in 2007. 4  The largest user within the manufacturing sector in 2005 was Paper manufacturing with total water withdrawals of 45%, or 2.56 km3, of the manufacturing share, followed by Primary metal industries with 28%, and Chemical manufacturing with 9% (Table 3.2).

As a group the manufacturing industries re-circulated just over one half of their water intake. In 2005, the Petroleum and coal product manufacturing industry had the highest recirculation rate at 140%—it reused water withdrawn from the environment more than any other manufacturing industry, before this water was either discharged or consumed by its manufacturing processes. The portion of intake water consumed by this industry, at 12%, was comparable to the rates of other industries in this sector (Table 3.2).

From 2005 to 2007, water intake decreased in 13 of the 16 industries surveyed (Table 3.3). Two manufacturing industries have notably higher water use than any other industries in this sector (Table 3.3). Water intake for the Paper manufacturing industry was 1,960 Mm3 in 2007 followed by 1,183 Mm3 for the Primary metal manufacturing industry. Industries with the next highest water intakes were Chemical manufacturing, with an intake of 437 Mm3, Petroleum and coal product manufacturing, with an intake of 373 Mm3, and Food manufacturing, with an intake of 291 Mm3 in 2007.


Wastewater refers to water that is returned to the environment after being used during some activity or process. Treatment to remove contaminants may occur before wastewater is discharged into the environment or it may be discharged untreated. Treatment can occur on-site, however wastewater discharged to a sanitary sewage system may travel long distances before it reaches a treatment system and is released into the environment.

Sewage systems carry more than domestic wastewater—they may also receive waste from the commercial, industrial and institutional sectors, as well as water that runs off of roofs and pavement and enters storm sewers. 5  More than three-quarters of Canadian households were connected to a municipal sewage collection system in 2006. 6  According to an inventory done in 2009 there are over 2,100 sewage treatment plants in Canada (Table 3.4).

Different wastewater treatment systems provide varying levels of wastewater treatment, using physical, biological and chemical processes. Primary treatment involves basic sedimentation of solid materials. Secondary and tertiary treatment can use a variety of other processes to improve effluent quality, including secondary sedimentation (aeration), filtration, nutrient removal and disinfection. In 2004, wastewater treatment was at secondary level or better, for approximately 74% of the population connected to sanitary sewers. 7  Larger communities are more likely to have higher levels of wastewater treatment.

Some substances are difficult to remove from wastewater. For example, scientists have discovered residues from pharmaceutical products in bodies of water. 8  These substances may be excreted or flushed down the drain, ending up in wastewater and ultimately in rivers and lakes. In 2005, 11% of households with leftover or expired medications reported that they disposed of these drugs by flushing them down the drain or toilet or burying them. 9 

In 2006, 19% of Canadian households not living in apartments used private septic systems. 10  Septic systems release nitrogen and phosphorus into the environment, and can be a source of groundwater contamination. However, septic tank maintenance can minimize these environmental impacts. In 2006, one-quarter of households with septic systems reported they performed maintenance every four or more years, 43% reported performing maintenance every two to three years, and 21% performed maintenance at least annually. Six percent of households reported they had never pumped or maintained their septic system. 10  The Canadian Mortgage and Housing Corporation recommends that maintenance be done every three to five years or when one-third of the tank volume is filled with solids. 11 

Industry is also a major water user and often needs to treat effluent prior to discharge. In 2006, industry invested $249 million on pollution abatement and control to reduce pollution of surface water. 12  The Manufacturing, Mineral extraction and Thermal-electric power generation industries discharged 32,793 Mm3 of water in 2007. Thermal-electric plants were responsible for the majority (83%) of this discharge. Most water (88%) was discharged into surface water bodies and was not treated before discharge. 3 

Manufacturers discharged 4,122 Mm3 of water in 2007, mostly into surface water bodies (77%) and into public sewer systems (11%). 4  Of the water discharged by manufacturers, 33% was not treated before being released. Seventeen percent of effluent received primary treatment, 44% underwent secondary or biological treatment and 7% underwent tertiary treatment.

Mineral extraction industries discharged 755 Mm3 of water in 2007. Most of this wastewater was discharged into surface water bodies (66%), with 16% going into groundwater and 11% into tailing ponds. More than half the wastewater discharged into surface water bodies and groundwater was not treated. 3 


Drinking water plants treat water that is supplied to commercial, institutional, industrial and residential users. In the residential sector, water is distributed to households for personal use, and some examples of how this water is used include drinking, bathing, cleaning, and watering lawns. In 2007, 86% of households received their water from a municipal water supply and 12% had a private well. 13 

According to an inventory of drinking water plants that serve communities of 300 or more people, there were more than 2,000 drinking water plants in Canada in 2009 (Table 3.4), serving 28 million Canadians. Drinking water plants, and the associated distribution systems, are run by water utility operators, who test and treat water to ensure it is safe for human consumption. Provincial and territorial governments have enacted legislation to ensure safe and high-quality drinking water based on Health Canada published Guidelines for Canadian Drinking Water Quality14 , 15  Approximately 88% of water processed by drinking water plants was from surface water sources, 10% was from groundwater and 2% was from groundwater under the direct influence of surface water (GUDI). 1 

In 2007, $807 million were spent on operation and maintenance for the acquisition and treatment of water at drinking water plants. The largest component of these expenses was labour ($302 million), while materials and energy costs represented $198 million and $199 million, respectively. 1 

Water withdrawals for the residential sector were the third largest overall with 9% of total water use (3.8 km3) in 2005 (Table 3.1). This volume represents a per capita residential water use of 117 m3 per year or 320 litres per person per day (L/day) in 2005. This value overestimates household use however, as some of the water allocated to the residential sector is used by other sectors of the economy, such as businesses or institutions. Additionally, national estimates of leakages from water distribution systems are difficult to determine as some provinces do not meter water to the same extent as others. Quebec is one of the most populated provinces in Canada but only meters 17% of residential clients and 37% of business clients using public water utilities. 16  The National Water and Wastewater Benchmarking Initiative looked at water use in households supplied by 34 water utilities across Canada, and found that the median volume of water used was 243 L /day in 2007. 17 

Conventional plants and direct filtration plants produced 55% of treated water in 2007, and provided water to 16.5 million people. Conventional water treatment has been established for over 100 years, and was responsible for treatment of 47% of water produced by drinking water plants in Canada in 2007. Conventional and direct filtration treatment plants use various physical and chemical processes to filter water. The only difference between the two is that conventional plants use sedimentation processes, while direct filtration plants do not. 18  These plants also use processes of disinfection, typically chlorination, to destroy pathogens in the water. A further 24% of water is treated using disinfection processes without filtration. Other more advanced membrane filtration technologies were used in the production of 4% of treated water. In 2007 operating and maintenance costs for conventional and direct filtration plants were $161 and $139 per thousand cubic metres of production, while these costs for systems that used only membrane filtration were $315 per thousand cubic metres of production. 1 


The agricultural sector was responsible for 4.6% (almost 2 km3) of total water withdrawals in 2005 (Table 3.1). The bulk of this water was used to irrigate crops, with a balance of 16% going to support livestock production.

Crops rely on soil moisture for growth. Soil moisture is replenished by precipitation or through irrigation. Irrigation helps to make up for a lack of moisture in the soil during periods of little rain, and contributes to higher and more predictable crop yields. While most crops in Canada are rain-fed, some are dependent on irrigation.

According to the 2006 Census of Agriculture, 844,975 hectares of farmland were irrigated in Canada in 2005. 19  In 2007, according to the Agricultural Water Use Survey, the bulk of irrigation withdrawals occurred in the more arid Western regions. Sixty percent of the area irrigated in Canada was found in Alberta, followed by British Columbia (13%) and Saskatchewan (12%) (Chart 3.1). Farms in Alberta also used more water per unit of irrigated land than farms in other provinces. Alberta was also the lead water user when it came to the volume of water used for irrigation, accounting for 73% of the total volume of water used for irrigation in 2007 (Chart 3.1). Together, British Columbia and Saskatchewan used an additional 20%. In comparison, farms in the Atlantic provinces and Quebec used very little water for irrigation. Agriculture occurs in these provinces, but farms tend to receive more rainfall than their counterparts to the west.

System of Environmental–Economic Accounting for Water (SEEA-W)

The System of Integrated Environmental and Economic Accounting, 20  developed by the United Nations, brings together economic and environmental information in a common framework to measure the contribution of the environment to the economy and the impact of the economy on the environment. A number of different types of accounts, including stocks, assets, and flows, are described in this system, and these accounts can be measured in physical or monetary terms. The data presented in Table 3.1 are physical flows of water and document national water use for the whole economy. Returns of water from the economy to the environment are included for manufacturing industries (Table 3.2).

Abstraction is defined as the amount of water used for the purpose of production and consumption activities, and includes water abstracted from the soil, and water used for hydro-electric generation. Furthermore, once the water used in the generation of hydro-electricity is returned to the environment it is to be included in subsequent abstraction downstream. The implication for hydro-electric generation is that the same volume of water can be counted several times as it passes through successive downstream turbines. Water resources are defined as the water found in fresh and brackish surface water and groundwater bodies within the national territory. The water of the oceans and open seas is excluded on the grounds that the volumes involved are so enormous that any measure of their stock becomes meaningless and that extraction for human use has no measurable impact on these volumes.

Source(s): United Nations Statistics Division, 2007, System of Environmental-Economic Accounting for Water, (accessed August 10, 2010).

The international water accounting guidelines (Textbox: "System of Integrated Environmental and Economic Accounting for Water") uses the term ‘abstracted water’ to measure both water used by crops that falls as precipitation and water applied through irrigation. Irrigation estimates reflect only the water withdrawn from a water body and applied to crops, while water abstraction is a calculation of all the water that contributes to the crop production. Estimates were calculated, with crop yield data and coefficients specific to Canada, to determine how much water the environment contributed to crop growth, i.e. to estimate how much water was required by crops.

In 2005, irrigation accounted for only 1.8% of the total abstracted water that contributed to crop growth. 21  Water requirements vary by crop type, with wheat, oilseed and feed grain using the most water in both 2005 and 2007 due to the large area of these crops that was planted (Table 3.5). The decrease in water embedded in crops in 2007 can be explained by lower wheat yields. In 2007, wheat yields were down 400 kg compared to the 2,700 kg per hectare realized in 2005. 22  In 2005, the precipitation that supported crop growth was roughly twice the volume of water that was withdrawn annually by all sectors of the economy (Table 3.1).

In-stream water use

Sectors that use in-stream water are also very important to the Canadian economy. Results of the Travel Activity and Motivation Survey indicated that 31% of adult Canadians reported swimming or boating while on an out-of-town, leisure trip of one or more nights in 2004 or 2005, and 27% reported that this activity was the main reason for taking at least one trip in those two years. 23  Similarly, 18% of adult Canadians went fishing while on an out-of-town trip of one or more nights in 2004 or 2005, and 49% reported that fishing was the main reason for taking at least one trip in those two years. 24 

Dams and reservoirs

The first large dam in Canada (the Jones Falls Masonry Dam on the Rideau Canal in Ontario) was completed in 1832. However, it was the development of commercial hydro-electric power in the early 1900s that resulted in the growth in the number of these massive structures. 25  In 2008, hydro-electricity represented 62% of all electricity generated in Canada. 26 

The Daniel Johnson Dam, with 12 generating units capable of producing 2,660 MW of electricity, 27  holds the largest reservoir by volume in Canada. This reservoir, located on the Manicouagan River in Quebec, has a gross capacity of 142 km3 of water, making it one of the largest in the world. 25 

In recent years, the creation of tailing ponds has become an important new reason for building large dams. 28 

Water transportation and fishing

Water transportation and fishing are important in-stream water uses. Shipping relies on both natural water ways and canal systems. In 2007, 468.6 million tonnes of freight were handled and 38 million passengers were carried across Canadian waters (Table 3.6). Forty-one percent of this freight was handled by Canadian ports in the Great Lakes and St. Lawrence regions. 29 , 30 

Fishing includes commercial and recreational activities. Commercial fish landings from freshwater sources contribute to the Canadian food supply, and are also exported. In 2007, 32,303 tonnes were caught and landed nationally (Table 3.7). In 2005, recreational fishers spent a total of 39.8 million days fishing in Canada—90% were Canadians and 10% were non-Canadians. Anglers who fished within the same jurisdiction as they lived spent an average of 15.4 days fishing in 2005, while tourists from outside the country fished for an average of 7 days. 31 


Table 3.6

Using final demand to estimate virtual water content

The virtual water associated with a commodity, an industry or even the entire economy of a nation, expresses the amount of water that has contributed to economic production. It makes water use explicit, and also allows comparisons of the amount of water required to produce commodities in different locations. Furthermore, looking at the virtual water content of a nation’s exports provides insight into how this natural resource is being drawn on and allows some quantification of how it contributes to the economy.

Industry uses water as part of the process of providing goods and services to consumers. By using the industry and commodity relationships detailed in the input-output model (Textbox: “Application of the Input-output model to water use”), it is possible to associate industrial uses of water with the commodities that are produced and with the consumers that purchase those commodities. 32  These final deliveries to consumers in the economy are termed final demand (Textbox: “Final demand”).

According to the United Nations System of Integrated Environmental–Economic Accounting for Water (SEEA-W), total water use includes water that is directly abstracted and water that is received from other economic units (Textbox: “System of Integrated Environmental–Economic Accounting for Water”). This accounting includes water-use for hydro-electric generation and the water absorbed by forests and agricultural crops, from both irrigation and precipitation.

Application of the Input-output model to water use

The data used to produce estimates of the water use to satisfy final demand are derived from Statistics Canada's Material and Energy Flow Accounts (MEFA), which integrate environmental data with the economic data from the Canadian System of National Accounts (CSNA). The CSNA is the source of a number of Statistics Canada's most important indicators of economic activity, including gross domestic product. The input-output (I/O) accounts are one of the main components of the CSNA, and produce highly detailed production and consumption statistics for 303 industries, 719 goods and services and 170 categories of final demand.

The MEFA follow the I/O accounting framework to track the use of water by each industry and final demand sector. The flows are linked through the common industrial and commodity classification of the I/O tables. This linkage allows analysis of the interplay between economic activity and water use.

Final demand

Domestic demand

Personal expenditure: Household spending on new consumer goods and on consumer services, plus any mark-up on used goods. This includes expenditures by individuals, families and private non-profit organizations serving households.

Machinery and equipment: Capital expenditures on durable, tangible goods with an expected service life of one year or more, such as furniture, motor vehicles, office machines and equipment not permanently installed (permanently built-in equipment belongs to non-residential construction). Includes installation and delivery costs.

Construction: Construction of industrial, commercial and institutional buildings, dwellings, garages, cottages and mobile homes. Includes new construction, conversions resulting in a structural change, major renovations, permanently built-in equipment and site preparation.

Government expenditure: Economic activities of the federal government (including defence), the provincial and territorial governments, local (municipal) governments, universities, colleges, vocational and trade schools, publicly funded hospitals and residential care facilities, and publicly funded schools and school boards.

Inventories: Stocks of outputs that are still held by the units that produced them prior to their being further processed, sold or delivered to other units or used in other ways, and stocks of products acquired from other units that are intended to be used for intermediate consumption or for resale without further processing.

External demand

Exports: The sale of goods and services to buyers in other countries. Services include travel, freight and shipping, business services, government transactions, financial intermediation and other services.

Source(s): Statistics Canada, 2008, Guide to the Income and Expenditure Accounts, Catalogue no. 13-017-X.

Water use to supply final demand

Canada is one of the largest producers of hydro-electricity in the world. In 2008, hydro-electricity represented 62% of all electricity generated in Canada (Table 3.8). The volume of water used for hydro-electric generation in Canada is many times larger than all other uses of water in the country. Hydro-electric generation in Canada made use of approximately 3 trillion cubic metres of water in 2005. 21  This is more than 100 times the volume of water used by the Thermal-electric power generation sector, and just over 70 times the total volume of all water used in Canada in 2005 (Table 3.1).

Including hydro-electric water use in the analysis of water use elevates the importance of the use of electricity in the estimates. Any use of electricity in provinces with hydro-electric generation triggers large amounts of indirect water use by the electricity consumers. The proportion that utilities contribute to personal expenditure and exports increases considerably if in-stream water used for hydro-electric generation is included (Table 3.9). Including this volume in the water use estimates quickly changes the story of water use into a story of electricity consumption.

The following analysis estimates water use to satisfy final demand, and excludes the water used for hydro-electric generation. Estimates are shown with and without precipitation to allow for the comparison of the use of water provided by the environment (an ecosystem service) with the water withdrawn from the environment. For details of the methodology please consult the textbox “Estimates of abstracted water”.

When water used to generate hydro-electricity was excluded the total domestic demand for water decreased by 82%. When precipitation was also excluded, domestic demand for water was only 1.1% of the water use value that included hydro and precipitation (Table 3.10). Personal expenditures were the largest contributor to water use from a demand perspective—industrial production to meet household demand for goods and services was the cause of 47% of water use.

Estimates of abstracted water

The estimates of industrial water use include both water extracted by drinking water plants and provided to industry, and water extracted by industries for their own use. 3 

Estimates of the amount of water that supports agricultural production are detailed in Section 3.1.1 under Agriculture, and in Table 3.5.

For forestry, Natural Resources Canada estimates that approximately 4,000 m3 of water are required per hectare (ha) each year to maintain the trees on forested land. 33  This is equivalent to a water abstraction estimate of about 500 million m3 when applied to the 128.7 million ha of productive, accessible and non-reserved forest land. 34  This figure represents the total amount of water required to maintain the productive stock of trees in Canada, from which timber is extracted to contribute to the economy.

The challenge in estimating forest water use is compounded by conceptual issues related to water flows through time. Clearly, the entire forest is not harvested each year, so the amount of water flowing through that total area is not representative of the water required to produce a given year’s timber harvest. Instead, the virtual water related to a given quantity of harvested wood is represented by the total amount of water required throughout the lifetime of the tree prior to harvesting. Based on figures from Natural Resources Canada, the 2005 timber harvest of 203,325,000 m3 required between 400 and 600 billion m3 of lifetime water uptake. Thus the estimate of 500 km3 of water used for forestry approximates both the current flow estimate for the entire productive, non-reserved accessible area, and the virtual water content of the harvested wood.

Water use to satisfy domestic demand

Households use water directly whenever a tap is turned on. Water is used indirectly when goods and services are purchased that contain water, or are produced using water. Direct water use is a small portion of total household water requirements. It is either 3.7% or 17.3% of total water use depending whether or not precipitation is included in the analysis (Table 3.11).

The inclusion or exclusion of precipitation in the calculations is one way of illustrating the contribution that the natural environment makes to our economy. Without precipitation the production of many exports would not be possible, but typically water in this form is not acknowledged as an input. Further delineation and description of these ecosystem services is needed in order to fully understand the interaction between human activity and the environment.

When precipitation is included, manufactured products other than food account for 36.8% of the domestic demand for water—compared with only 3.6% when precipitation is not included. This reflects both the prevalence of wood and paper products in domestically consumed manufactured goods, and the large amount of water required by forests. Manufacturing of forest products contributed $25.8 billion to Canada’s gross domestic product (GDP) in 2005, almost 14% of all manufacturing. 35 

Food products, which accounted for 10% of manufacturing GDP in 2005, 35  and which also require large amounts of water to produce, accounted for 30% of household indirect water use. When precipitation was excluded, electricity consumption triggered the largest indirect water use by households because it is used in Thermal-electric power generation.

Water use to satisfy demand for exports

When precipitation was included, exports required a much larger proportion of total water use, largely due to the water requirements of agricultural crops and trees (Table 3.10). In 2005, exports of forest products amounted to $37.5 billion or 8.6% of total exports, and exports of agricultural commodities amounted to $25.7 billion or 5.9% of total exports. 36  More water however is embedded in forest products than food: the production of exported lumber, wood pulp, paper, and other forest products required seven times more water than the production of exported agricultural commodities. When precipitation was not considered, the share of the Other manufactured goods category decreased, and the Utilities category increased, again because of water use by the Thermal-electric power generation sector (Table 3.12).

Relationship between water supply and demand in Canada

As shown in Sections 1 and 2, Canada is endowed with large volumes of renewable freshwater but this supply is unevenly distributed and changing over time. As presented earlier in this section, every aspect of Canada’s society relies on water, placing demands on our water resources. The following analysis combines demand and supply by looking at water intake, a proxy for demand, as a proportion of water yield.

The relationship between the timing of demand and supply can be an indicator of the pressure exerted on water resources. When renewable water resources are insufficient to satisfy demand people increase their use of water stocks.

In 2005, total water withdrawals in Canada amounted to 1.2% of the average annual renewable water resources. More pressure, however, was placed on water resources in some areas of the country than in others, with this pressure peaking in summer. Hydrographs presented in Chart 2.6 demonstrate that monthly water yield is lowest in August, which generally coincides with peak municipal demand.

This relationship between supply and demand is illustrated in Map 3.1, which compares water intake for August 2005 with the 34-year median water yield for August by drainage region. The information presented in this map was compiled from Statistics Canada surveys that collected water intake data from Manufacturing, Thermal- electric power generation, Mining and Agriculture (irrigation) industries and from drinking water plants, as well as data on household reliance on non-municipal water. Water intake from the Oil and gas industry was not included in this analysis, as the data for this industry could not be compiled by drainage region. Intake from all sectors was summed for the country by drainage region, divided by the water yield produced in each drainage region, and presented as a categorized ratio.

Greater pressure was exerted on water resources in the Okanagan–Similkameen (drainage region 3), and the Prairies (drainage regions 9, 11 and 12)—where water yield is generally low (Map 3.1). In the Prairies, where stocks are limited, water demand must be met primarily by renewable water, and water shortages are evident when demand exceeds the renewable supply.

The North Saskatchewan (drainage region 10) does not show a similar demand-to-supply ratio to that of the South Saskatchewan (drainage region 11) because it has a higher water yield (Table 2.2), a smaller population (Table 2.3) and less irrigation.

Greater pressure was also noted in the Great Lakes (drainage region 19) and St. Lawrence (drainage region 21)—where population density is highest (Chart 2.1, Table 2.3). The high ratio for the Great lakes (drainage region 19) can be explained by the large volumes of water withdrawn by the Thermal-electric power generation industry that provides power to this region. In contrast, the demands for electricity in the St. Lawrence (drainage region 21) are largely met by hydro-electric power generation—an in-stream water use that was not considered in this analysis.

Even though the Great Lakes drainage region (region 19) has a slightly lower per capita water yield in 2006 (Table 2.3), its residents may not have the same awareness of pressure exerted on their water resources as residents of the Okanagan–Similkameen (drainage region 3). When more freshwater is withdrawn than is generated by the renewable flow within an area, the remainder must be removed from its lake, river and groundwater stocks. In drainage regions 19, 20, and 21 there are significantly more reserves, in the form of the Great Lakes and St. Lawrence River, than are found in the Prairies and interior of British Columbia. The Great Lakes contain more than 6.5 times Canada’s total water yield, but less than 1% of this volume is renewed each year. 37  Therefore in the Great Lakes region, where renewable supply is supplemented with stock water, it is less evident when needs are not met through renewable water resources.

Since demand for water is not synchronized with supply, data are needed by geographic region and at a time scale that allows tracking of water use and monitoring of water resources.