List of longest rivers of Canada
Nine rivers in this list cross international boundaries or form them. Four—the Yukon, Columbia, Porcupine, and Kootenay—begin in Canada and flow into the United States. Five—the Milk, Pend d'Oreille, Saint Lawrence, Red, and Saint John—begin in the United States and flow into Canada. Of these, the Milk and the Kootenay cross the international border twice, the Milk leaving and then re-entering the United States, the Kootenay leaving and then re-entering Canada. The drainage basins of these nine rivers extend into both countries; in addition, the drainage basins of six others—the Fraser, Assiniboine, South Saskatchewan, Saskatchewan, Nelson, and Winnipeg—extend into the United States even though their main stems flow entirely within Canada.
Water supply and sanitation in Canada
Metro Vancouver's water system is one of the largest in North America. Almost 600 square kilometers of mountainous land is closed to public access to protect the large reservoirs which collect rain and snow melt. 
Three watersheds - the Capilano, Seymour and Coquitlam Watersheds are the water source for more than two million residents in the most populated urban region of British Columbia. Each watershed supplies about one-third of the region’s tap water. The regional district’s long-standing closed watershed policy is one component of a water supply system that provides multiple barriers to contamination, from source to tap.