Water: How much do we have?

Global

- About 70% of the earth is covered in water.

- The total amount of water in the world is approximately 1.4 billion km3, of which 97.5% is saltwater and 2.5% is fresh water.

 - Of the 35 million km3 of freshwater on earth, about 24.4 million km3 are locked up in the form of glacial ice, permafrost, or permanent snow. Groundwater and soil moisture account for 10.7 million km3. Freshwater lakes and marshlands hold about 0.1 million km3. Rivers, the most visible form of fresh water account for 0.002 million km3 or about less than 0.01% of all forms of fresh water.

 - The major source of fresh water is evaporation off the surface of the oceans, approximately 505 000 km3 a year. Another 72 000 km3 evaporates from land surfaces annually.

- Approximately 80% of all precipitation (about 458 000 km3) falls on the oceans, the remaining 20% (119 000 km3) falls over land. The difference between precipitation onto land surfaces and evaporation from those surfaces is runoff and groundwater recharge – approximately 47 000 km3 per year.

- Brazil is the country with the most renewable fresh water. Canada is third after Russia.

- Ninety-nine percent of surface freshwater by volume is in lakes and only one percent in rivers.

- Of all fresh water not locked up in ice caps or glaciers, some 20% is in areas too remote for humans to access and of the remaining 80% about three-quarters comes at the wrong time and place – in monsoons and floods – and is not always captured for use by people. The remainder is less than 0.08 of 1% of the total water on the planet. Expressed another way, if all the earth's water were stored in a 5-litre container, available fresh water would not quite fill a teaspoon.

 - There are some 100 million lakes between 1 hectare (0.01 km2) and 1 km2 in area and about one million lakes which are greater than 1 km2 in area.

 - The lake with the largest surface area in the world is the Caspian Sea (about 436 000 km2) followed by Lake Superior (about 82 300 km2).

 - The deepest lake is Lake Baikal (about 1 700 metres deep) followed by Lake Tanganyika (about 1 400 metres deep).

- The largest river basin in the world, by drainage basin size and by discharge, is the Amazon.

- The Nile River is the world's longest river. It flows 6 670 kilometres from its headwaters to the Mediterranean Sea.

- Although 60% of the world's population live in Asia, the continent has only 36% of the world's water resources.

- Water stress begins when there is less than 1 700 m3 of water per person per year for all major functions (domestic, industrial, agricultural, and natural ecosystems) and becomes severe when there is less than 1 000 m3 per person.

 - Currently, 600 million people face water scarcity. Depending on future rates of population growth, between 2.7 billion and 3.2 billion people may be living in either water-scarce or water-stressed conditions by 2025.

 - At times, the flow is so low in some of the world's largest rivers – the Amu Darya and Syr Darya in central Asia, the Yellow River in China, the Colorado River in the United States, the Indus River between India and Pakistan – that they do not reach the sea.

 - The Aral Sea was once the world's fourth largest lake; now it's the site of aquatic ruin. It's lost two-thirds of its surface area, some 60 000 fishing jobs have been wiped out, and people living in the salty and toxic surroundings suffer from a variety of ailments.

 - The world's wetland area was halved during the 20th century. In some locations wetlands are worth as much as $20 000 per hectare (0.01 km2).

 - The most devastating floods have occurred on the Yellow River in China. In 1887, 900 000 lives were lost and in 1938, 870 000. In each of 1911, 1931, and 1935 at least 100 000 lives were lost in the Yangtze River basin in China.

 - More than 2 200 major and minor water-related natural disasters occurred in the world between 1990 and 2001. Asia and Africa were the most affected continents, with floods accounting for half of these disasters.

 Canada

 - Annually, Canada's rivers discharge 105 000 m3/s, 7% of the world's renewable water supply.

 - Almost 9%, or 891 163 km2, of Canada's total area is covered by freshwater.

 - The Canadian portion of the Great Lakes occupies nearly 10%, or 87 500 km2, of the 891 163 km2 freshwater area in Canada.

 - Approximately 60% of Canada's fresh water drains to the north, while 85% of the population lives along the southern border with the United States.

 - Canada has about 25% of the world's wetlands – the largest wetland area in the world.

 - Wetlands totaling an area of more than 1.2 million km2 (127 million hectares) cover about 14% of the land area of Canada.

 - Henderson Lake, British Columbia, has the greatest average annual precipitation in Canada – 6 655 millimetres. In contrast Eureka, in Nunavut, has the least average annual precipitation – 64 millimetres.

 - An estimated area of 200 000 km2, or about 2% of the country's area is covered by glaciers and icefields.

 - The largest river basin in Canada is the Mackenzie based on drainage area, discharge and length.

 - The Great Lakes are the largest system of fresh, surface water on earth, containing roughly 18 percent of the world's fresh surface water.

 - The Great Lakes Basin (shared with the United States) is the world's largest freshwater lake system.

 - The largest lake entirely in Canada is Great Bear Lake in the Northwest Territories, measuring 31 328 km2.

 - The deepest lake in Canada is Great Slave Lake, N.W.T., 614 metres.

 - There are an estimated 2 million lakes in Canada covering approximately 7.6% of Canada's land area.

 - Canada has more lake area than any other country in the world.

 - There are more than 31 000 freshwater lakes in Canada that are larger than 3 km2 in area; about 560 are more than 100 km2. Many smaller lakes dot the landscape.

- The most common causes of flooding in Canada are water backing up behind ice jams and the rapid melting of heavy winter snow cover, particularly when accompanied by rainfall. Heavy rainfall itself can also cause floods.

- The 1996 Saguenay basin storm and associated flood in Quebec led to 10 deaths and over $1500 million in damages.

 - The 1997 Red River flood in Manitoba caused damages estimated at approximately $815 million.

 - As a general rule, when water velocity doubles, its erosive power increases four-fold and its capacity to carry sediments increases by 64 times. Eroded sediments are eventually deposited in wetlands, lakes, or river pools, reducing channel capacity and affecting fish habitat.

- Dry regions in the interior of British Columbia and in the southern Prairies have severe soil moisture deficits at some time during most summers and can suffer from long-term drought conditions. These areas hold most of the 1 million hectares (10 000 km2) of irrigated cropland in Canada, with Alberta alone accounting for 60%.

 - The development of storage reservoirs and dugouts is essential to maintaining adequate year-round water supplies, particularly in the drier parts of the country. There are about 155 000 dugouts and 21 500 reservoirs in western Canada to supply sufficient water for rural areas.

 - Dugouts are typically artificial ponds that are 4 to 6 metres deep with a capacity of 2000 to 6000 m3, designed to provide a 2-year water supply with allowance for evaporation losses and ice formation.

 - In 2004, about 28% of Canadian municipalities with water distribution systems reported problems with water availability within the previous five years.

http://www.ec.gc.ca/water/en/info/facts/e_quantity.htm