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As GEO-1 demonstrated, North America has an abundant supply of freshwater resources but it is unequally distributed across the region. Surface and groundwater sources together provide an annual 5 308 km3 of renewable and fossil water to the two countries, which is about 13 per cent of the global total (WRI, UNEP, UNDP and WB 1998). On a per capita basis, Canada has 10 times more water resources than the United States. However, water scarcities occur in many parts of North America, including some parts of Canada's prairie provinces and the US southwest (OECD 1995, 1996).
Over the past 100 years, the demand for water has increased steadily in North America. This is partly a result of population growth and increasing municipal demands for water. It is also related to North America's energy-intensive industrial development and the dramatic expansion of irrigated agriculture. The latter has occurred mainly in the United States where the area of irrigated land has risen from 1.5 million hectares in 1890 to approximately 21 million hectares in 1995 (Council on Environmental Quality 1997). Dams and diversion projects have flourished over the past century, as communities and economic sectors have sought access to secure water supplies. Meanwhile, water has been pumped from some underground aquifers faster than natural recharge rates, depleting an important resource and causing water tables in the United States to fall by up to 120 cm a year in some irrigated regions (Pimentel and others 1997). Cotton farming has had major effects on water supplies in northern Texas and parts of New Mexico, for instance. These areas were traditionally used for cattle ranching but large-scale agriculture was made possible with the advent of groundwater irrigation. Cotton farming then increased demands for water from the Ogallala aquifer and led to severe groundwater depletion (Kasperson and others 1996).
During the 1990s, several measures have been taken to increase water use efficiency. As a result, per capita water use has not risen much in North America. In fact, Canada reported a 3.3 per cent decrease in daily municipal per capita water use between 1991 and 1994 - equivalent to a reduction of 22 litres per person per day (Government of Canada 1996). Nevertheless, Canada and the United States still rank among the world's largest consumers of water: average annual per capita withdrawal of water resources was 1 798 m3 for North America (1991 data), in contrast with 645 m3 for the world (1987), 625 m3 for Europe (1995), and 202 m3 for Africa (1995) (WRI, UNEP, UNDP and WB 1998).
Although the municipal supply, demand and quality of water receive much attention, the sectors that use most water in North America are agriculture and power generation (see pie charts left). In the United States, each accounts for about 40 per cent of total water withdrawal. In Canada, the figures are 58 per cent for power generation and 7 per cent for agriculture (OECD 1996 and 1995). Recently, however, these withdrawals have been declining while domestic use has been rising - it has almost doubled since 1960, reflecting population growth and urban expansion (OECD 1996).
The growth of municipal and industrial demands for water has led to conflicts over the distribution of water rights. Water resources are now a major constraint to growth and increased economic activities envisioned by planners, especially in the west and southwestern arid lands of the United States (Council on Environmental Quality 1997). Agricultural consumption accounts for a large share of water use in these areas. At the same time, demands for recreation, aesthetic enjoyment and wildlife habitat have become increasingly important in the management of North America's water resources. Both commercial and recreational fishing are also important water uses. Conflicting demands for water have prompted many to favour the establishment of water management boards, in combination with water conservation measures.
The domestic water and sewer systems introduced for urban areas early in this century greatly improved the quality of drinking water and reduced the incidence of water-borne disease. Over the past decade, the quality of drinking water in North America has been improved still further. In 1994, more than 80 per cent of community water systems, serving 240 million people, reported no violations of health-based standards. Even so, in the same year more than 40 million people in the United States obtained their drinking water from a system in which there were violations of health-based standards (Council on Environmental Quality 1997). Canada also enjoys relatively high-quality water (Government of Canada 1996). However, some groundwater, which more than six million Canadians rely on for their water supplies, may be contaminated as a result of poor earlier management of wastes or industrial chemicals. Because groundwater moves slowly, detection of such contamination is often long delayed - sometimes until well after the source of the contamination has disappeared. Well water is often affected by faecal coliform bacteria and nitrates, which may be present in 20-40 per cent of all rural wells in Canada (Government of Canada 1996).
The International Joint Commission states that boundary areas are vulnerable to impairment from toxic chemical use: 'The Great Lakes region, acting as a sink for many persistent, bioaccumulative compounds, is the most prominent example. While there has been progress in curbing use of the most harmful compounds and in restoring contaminated areas since the 1970s, releases persist. A 1995 analysis by Environment Canada showed that Great Lakes basin industries released 173 092 tons of materials listed on the Canadian National Pollutant Release Inventory or the US Toxic Release Inventory in one year. When air releases originating on both sides of the border within the “one-day airshed” of the basin were taken into account, the total nearly doubled to 319 098 tons' (International Joint Commission 1997, Environment Canada 1995).
In some parts of North America, especially in older cities where sanitary and storm water networks are combined and become overcharged in wet weather, wastewater is still discharged into water bodies without treatment (OECD 1996). Many rural and indigenous populations, unconnected to municipal supplies and dependent on well water, experience water quality problems. As recently as the mid-1980s, half the homes on indigenous people's reserves in Canada were without running water, sewers or septic tanks. Significant progress has been made, with about 96 per cent of homes in 1996-97 having some form of potable water supply, and almost 92 per cent of homes with sewage disposal facilities (Minister of Public Works and Government Services, Canada, 1998). More specific examples were cited in GEO-1.
Significant achievements have been made in reducing industrial pollutants in the United States - for example, through the Federal Water Pollution Control Act of 1956, as amended by bills such as the Clean Water Act of 1977. However, as the scope of economic activity widens, new pollutants are introduced to water supplies. Agrochemical run-off is the main source of water pollution in agricultural regions of North America, contributing 60 per cent of the total impaired stream length and 57 per cent of impaired lake surface in the United States (OECD 1996). Pesticide and herbicide run-off has contaminated groundwater in many areas and has been registered in most water bodies, including the Great Lakes and the St Lawrence, the Susquehanna and Colorado rivers. Nitrogen and phosphorus levels that exceed national standards have been found in the surface and groundwater of areas devoted to intensive agriculture, resulting in over-fertilization and the eutrophication of water bodies.
Fish consumption advisories provide another measure of water quality. In 1995, consumer advisories to limit consumption of certain fish species increased by 14 per cent over the previous year; advisories were issued in 1995 for 1740 water bodies in 47 states, an increase of 209 warnings from 1994 (Council on Environmental Quality 1997). Mercury accounted for more than two-thirds of the warnings. Warnings for PCBs rose 37 per cent, for chlordane 16 per cent and for DDT (which has been banned in the United States since 1972) by 3 per cent. These increases may result from the increased number of surveys being carried out by States and therefore do not necessarily indicate worsening conditions. However, they do show where local water quality problems exist (Council on Environmental Quality 1997).
Over the next 10 years, water use will continue to rise. Expanding populations will require more water to serve domestic, commercial, recreational and manufacturing needs (International Joint Commission 1997). Climate change is expected to further increase the demand for irrigation water in some areas of North America, especially the Great Plains.
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