With only 3% of water on earth being freshwater, life on earth depends upon the security and maintenance of this most valuable resource. Here in North America, we typically think of lakes and flowing rivers as our sources of freshwater—in particular the Great Lakes, which are shared between Canada and the United States. In fact, this couldn’t be further from the truth. In their book The changing earth: Exploring geology and evolution, J.S. Monroe and R. Wicander suggest that 97% of North America’s freshwater lies beneath the earth’s surface, in aquifers. This groundwater is used in varying degrees across North America. In Canada, for example, less than half of the population of Quebec rely on groundwater, whereas almost everyone on Prince Edward Island depends on groundwater for their drinking water. And from an agricultural perspective, over 75% of farms and ranches across Canada rely on groundwater for irrigation.
Despite the importance of groundwater reservoirs to North America, these supplies are under threat from over pumping and, in particular, pollution. Nitrates from pesticides and fertilizers have contaminated most groundwater that lies below agricultural land—though at present the level of pollution does not pose a health risk. And in urban areas, gasoline, oil and salt from winter gritting leeches into groundwater supplies and pollutes them. Salt is also a risk from rising sea levels. Some scientists suggest salt water is bound to infiltrate low-lying reservoirs of groundwater, rendering them unfit for human consumption.
Thankfully, there’s still hope, especially for Canada. With the country’s tiny population but large geographic size, most Canadian groundwater has yet to be affected by either over pumping or pollution. How Canada goes about managing and protecting this resource will have implications around the world.
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http://www.scienceadvice.ca/en/assessments/completed/groundwater.aspx
http://www.groundwater.org/gi/sourcesofgwcontam.html