Threats to Water Availability in Canada

The following chapter of Threats to Water Availability in Canada, published by the National Water Research Institute and the Meteorological Service of Canada, outlines the impacts of urban development on water resources.

Jiri Marsalek,1 W. Edgar Watt,2 Liz Lefrancois,3 Ben F. Boots4 and Stan Woods5

  1. Environment Canada, National Water Research Institute, Burlington, ON
  2. Queen’s University, Department of Civil Engineering, Kingston, ON
  3. Environment Canada, Water Awareness and Water Conservation, Ottawa, ON
  4. Buffalo Pound Water Administration Board, Regina, SK
  5. Greater Vancouver Regional District, Policy & Planning Department, Burnaby, BC

Current Status

Urban development interferes with water resources by altering the hydrological cycle and increasing demands on provision of water services in the affected areas. Changes in the hydrological cycle include altered fluxes of water, sediment, chemicals and microorganisms, and increased releases of waste heat. In general, such changes lead to flow and sediment regime changes, geomorphological changes, impaired water quality, reduced biodiversity and overall degradation of water resources. At the same time, growing urban populations impose increasing demands on provision of water services, including water supply, drainage, wastewater collection and management, and beneficial uses of receiving waters. Integrated urban water management is used to mitigate the conflicts between urban development demands on water services and the resulting impacts on local water resources. Specific aspects of urban development impacts on receiving waters and threats to water availability for municipal water supply are addressed in this chapter. Even though the emphasis was placed on water quantity and availability issues, certain aspects of water quality are also included where appropriate.

Impacts of Urban Development on Water Resources

The discussion of urban development impacts on water resources begins with impacts on water quantity, followed by those on water quality.

Compared to natural watersheds, the hydrological cycle in urban areas is significantly altered and changes may occur in the atmospheric phase, e.g., local meteorological phenomena and microclimate leading, for example, to increased precipitation downwind of cities, higher incidence of fog, and higher air temperatures.

Changes in the land phase include increased volumes and discharges of surface runoff, which contribute to flooding or water ponding (see also Chapter 4). There are related increases in soil erosion; changes in the sediment regime relating to sediment transport and deposition (siltation) and stream geomorphology; reduced evapotranspiration; reduced infiltration; groundwater pollution; thermal enhancement of receiving waters; densimetric stratification; and impacts on wetlands through drainage and pollution.

Groundwater recharge may decrease due to increased imperviousness, but such recharge losses may be partly offset by leakage from water pipes and sewers, and intentional infiltration of roof runoff or stormwater practised in some urban areas. The group American Rivers recently reported losses in groundwater recharge due to urban sprawl and increased catchment imperviousness: for the urban areas developing most rapidly during the period from 1982 to 1997 (e.g., Atlanta, Ga.), simple estimates of recharge reductions ranged from 200 to 500 million m3/year (American Rivers, 2002). Qualitatively similar findings would be found in fast growing Canadian urban areas.

Demands on water services lead to increased withdrawals from source waters, which may affect other receiving water uses relating to source apportionment, low and high flows, stream habitat and ecology, and groundwater levels. Return of flow/filter backwash and treatment plant residuals may contribute to water pollution. With respect to the collection and management of wastewaters, effluent disposal to receiving waters may cause pollution and affect the flow regime. Leaky sanitary/combined sewers may contribute to groundwater pollution.

Fundamental water regime changes caused by urban development affect instream water uses, such as recreation (swimming, boating, and fishing); operation of multipurpose reservoirs, with conflicting demands of water supply, recreation, hydropower generation and flood protection imposed on reservoir operation; and aesthetic and ecological functions of receiving waters.

Specific impacts of urban runoff (stormwater) on water quality and ecosystem health were addressed earlier in a companion report titled Threats to Sources of Drinking Water and Aquatic Ecosystem Health in Canada (Environment Canada, 2001) and are briefly summarized below.

Discharges of urban stormwater cause physical, chemical, microbiological and combined impacts on water quality.

Physical impacts include:

  • increased flow (the effects of which are flooding, erosion, habitat washout)
  • changes in sediment regime (habitat destruction, interference with water quality processes, impacts on aquatic life, transport of contaminants)
  • thermal energy inputs (thermal pollution, loss of cold water fisheries), and
  • densimetric stratification (impairment of vertical mixing and oxygenation of bottom water layers) (Marsalek et al., 2001).

Chemicals discharged with stormwater include:

  • biodegradable organics (contribute to dissolved oxygen depletion), nutrients (eutrophication), and
  • trace metals, chloride, persistent organic pollutants (POPs) and hydrocarbons (acute and chronic toxicity, and genotoxicity).
  • Microorganisms conveyed by stormwater include bacteria and viruses of fecal origin and their discharges contribute to beach closures and contamination of shellfish harvesting areas. Typically, combinations of physical, chemical and microbiological impacts are encountered in receiving waters and are measured by the performance of biological communities (Marsalek et al., 2001).
  • Discharges of municipal wastewater treatment plant effluents cause chemical, microbiological and combined impacts on receiving waters. The chemicals of concern in these effluents include:
  • conventional constituents (suspended solids, chemicals causing biochemical and chemical oxygen demand, nutrients)
  • toxicants (chlorine, ammonium, trace organics, trace metals), and
  • new chemicals of concern (endocrine disrupters, pharmaceutical and therapeutic products, antibiotics).

Microorganisms in the effluents include indicator bacteria, viruses, helminths and protozoa. The main impacts of municipal wastewater treatment effluent discharges include restrictions on fish and shellfish consumption, degradation of aquatic and wildlife populations and their habitat (including water and bottom sediment quality), eutrophication or undesirable algal growth, isolated incidents of waterborne diseases caused by sewage contamination of drinking water supplies, beach closures, degradation of aesthetics, and added costs to agricultural, industrial, and municipal users for treatment of water (Chambers et al., 1997).

Municipal wastewater effluent discharges may adversely affect the aquatic ecosystem by alterations of chemical dynamics, energy dynamics, food web (trophic dynamics), dispersal and migration, disturbance of ecosystem development, reduced biodiversity, loss of critical species, and reduced genetic diversity (Lijklema et al., 1993).

Threats to Municipal Water Supply

On a national basis, Canada has abundant sources of water and has been ranked second best in the world (after Finland) in a recent international survey of the Water Poverty Index (Sullivan, 2002). This index takes into consideration water resource (internal flows, external inflows, population), access (percentage of population served by water supply and sanitation, access to irrigation water), use (domestic, industrial and agricultural uses), capacity (the level of human and financial capacity to manage the system), and environment (indicator of ecological integrity, or adequacy of water resources for environmental needs). In spite of this favourable assessment of Canadian water resources, some communities in Canada have been experiencing water supply shortages, which are caused by water quantity and/or water quality problems. About 26% of municipalities with water supply systems reported water shortages during the 1994 to 1999 period, for such reasons as seasonal shortages due to droughts, infrastructure problems, and increased consumption. In a water use survey published by Environment Canada (2002b), municipalities dependent on municipal groundwater systems reported water shortages more frequently than did those relying on surface waters. Regional experience may differ from these national survey findings.

Municipal water use: The discussion of threats to municipal water supply begins with municipal use, followed by the issues related to the sources, treatment and distribution infrastructure. This sequence follows the multi-barrier approach to drinking water protection and is maintained throughout the whole chapter.

Municipal water use includes all water supplied by the municipal water system. It is categorized by Environment Canada (2002a) as residential, commercial, industrial and “other.” “Other” includes water lost through leakage; unaccounted-for-water uses, such as fire fighting or distribution system flushing; and, water that the municipality was unable to assign to one of the first three categories. The best indicators of water use in urban areas are municipal water use of 638 litres/capita/day (the 1999 national average for all municipal sectors) and residential water use of 343 litres/capita/day. The latter use accounts for more than half of all municipal water use in Canada and ranges from 240 to 460 litres/capita/day; much lower values can be found in northern Canada. (Environment Canada, 2002a,c).

According to the Organisation for Economic Cooperation and Development (OECD, 1999), Canada is among the largest per capita users of residential water among the developed nations and is in a group including the United States, Australia and Japan. It is important to note (Fig. 1) that municipal water use represents only 11% of all water use (withdrawals) in Canada, other major user sectors being agriculture, mining, manufacturing and thermal power generation.

1996 water use in Canada (Environment Canada, 2002b).

Municipal water supply sources: Selection of water supply source is based on such considerations as safe yield, water quality, collection requirements (intakes, wells), treatment requirements (including residue disposal), and transmission/distribution (Hamann et al., 1990). Both surface water bodies and aquifers are used to supply water to urban residents. Approximately 74% of Canadians use surface water and 26% use groundwater for water supply (Environment Canada, 2002b). For both surface waters and aquifers, sustainable withdrawals can be determined based on either lake levels, and/or stream levels, water table levels, streamflows, and water apportionment. Source water limitations force suppliers to access less desirable sources, e.g., in the Prairies, deeper wells that may have highly mineralized water.

For surface sources, this may require the use of more distant sources, or development of sources with lower water quality requiring more complex treatment entailing more losses in the treatment process. Stress on both surface water and groundwater sources may lead to service disruptions, which can often be mitigated by proactive demand side management (advisory bulletins, restrictions, pricing). New, but so far relatively minor, sources include (a) subpotable water obtained by wastewater and greywater reclamation and/or recycling, (b) rainwater, and (c) bottled drinking water.

Water treatment systems: Water treatment systems are required to make raw water drinkable. As high quality sources of water become depleted, municipalities are increasingly using lower quality source water requiring more treatment. However, depending on the causes of lower source water quality, this approach may increase human health risk in drinking water supply by increased reliance on technology and safe operation in drinking water supply. Equipment and/or operator failures may lead to serious consequences (O’Connor, 2002).

Another shortcoming of using lower quality source water arises because more complex treatment systems tend to consume more water in the treatment process, mostly in the form of wastewater and sludge produced in various treatment processes. The choice of the water treatment processes depends on: source quality, required finished water quality, reliability of process equipment, operational requirements, and staff qualifications and training. It must take into account changing source quality and equipment malfunctions, available land for construction of treatment facility, waste disposal constraints, and cost considerations (Hamann et al., 1990).

Typical treatment schemes for surface water and groundwater differ. Water quality problems associated with surface water quality include particulate levels, colour, taste and odour, and microbiological content. The treatment processes commonly applied include coagulation, flocculation, and sedimentation, followed by filtration and disinfection (Hamann et al., 1990). In groundwater, the main water quality problems include high hardness, iron and manganese contents. Treatment schemes may include lime or soda ash treatment, flocculation, filtration and disinfection.

Water distribution systems: Water distribution includes the entire infrastructure from the source water treatment outlet to the tap. On average, about 20% of total daily municipal water use is attributed mostly to distribution losses and also to unaccounted-for-water. It is further recognized that reported values of losses are generally underestimated and increase with the age of the distribution system. Many Canadian municipalities address the issue of losses, but to a varying extent ranging from reactive repairs to proactive loss management programs. A necessary component of unaccounted-for-water is that required by various operational measures including the flushing of pipes and reservoirs to maintain water quality in the distribution network. Focus on security of water reservoirs and distribution networks, in relation to protection against various threats and accidents, has increased substantially since 2001 (U.S. EPA, 2002).

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