Learning Objectives

  • Describe the distribution of Earth's water resources
  • Explain why freshwater is one of Earth's limited resources

What do you think of when you drink a glass of water?

Do you think about where that water may have come from? Probably not...

The water you're drinking may have been part of a rainstorm that pounded the earth long before life existed.

The water we have access to today has been around since before life existed billions of years ago. Water is essential to maintaining life on earth. Humans can survive months without food but only days without water.

Time for a quiz...

Global Water Distribution

What can we determine about the world's water distribution from the image above?

There is not a lot of fresh water found on earth. 71% of the earth's surface is covered in water but only 3% of this is made up of freshwater. An even smaller percentage of this is liquid fresh water that can be used by humans. The freshwater we use comes mainly from the following sources.

Surface Water

Surface water is fresh water on Earth's land surface. Surface water is found in the following locations as well as two of the three locations referenced prior.


Areas such as lakes, rivers, streams and wetlands have led to the development of what throughout history?

Some of the oldest cities in the world were built near rivers, lakes and streams. Today, most large cities depend on surface water for their water supplies. Rivers, lakes, aquifers, streams, reservoirs ....

...all provide drinking water, water to grow crops, provide food such as fish and shellfish, power for industry (what is the name of this power) and provide a means of transportation by boat.


Complete the assessment task in this link...

Click on this link to watch the video on Global Water Distribution. You will receive questions from this video on tomorrow's test.

Industrial Water Use

Industry accounts for 19% of water use. This includes manufacturing goods, disposing of waste and generating power.

1000 L of water is required to produce 1 Kg of aluminium. 500,000 L of water are needed to manufacture a car.

Most of the water used in industry is used to cool power plants. Power plant cooling systems usually pump water from a river or lake and carry it through pipes to the cooling tower before pumping the water back to the source. Although this water can be warmer than when it was first extracted, it's still relatively clean and can be reused.

Agricultural Water Use

It can take 300 L of water to produce one ear of corn. That's the equivalent of what the average American uses over the course of a day. Although agriculture makes up about 67% of the water used in the world, 80% of this water evaporates and never actually reaches plant roots. This is due to inefficient methods of irrigation.


Any ideas as to what this means?

Irrigation is the process of providing water to plants from other sources other than direct precipitation. The earliest form of irrigation may have involved flooding fields with water from a nearby river or stream.

Many different irrigation techniques are used today. Cotton is irrigated with shallow, water filled ditches. High pressure overhead sprinkler systems are another form of irrigation. The sprinkler system method is an inefficient use of water. Why do you think this might be? Why is it important that irrigation systems that use water more efficiently become more common in the agricultural world?

Water Management Projects

For thousands of years, humans have altered streams and rivers to make them more useful. The Romans built aqueducts to bring water from the mountains to the dry areas of Italy, France and Spain. Some of these aqueducts are still in use.

Our projects today are more complex and show a more acute understanding of human and ecological needs.

What types of irrigation systems do we have today that are designed to meet the needs of the people with inadequate water supplies?

These projects can make a dry area habitable, can create a reservoir for recreation, can provide drinking water or can generate electrical power. These types of methods have enabled habitation and agriculture in dry areas such as deserts. These can have both high costs in terms of finance and ecology.

Water Diversion Projects

The canal shown below diverts the Owens river in California to provide drinking water for Los Angeles.

The Colorado river is diverted to provide drinking water for states such as Arizona, Utah and California.

Dams and Rerservoirs

Dams are built across rivers to control the flow. When a river is dammed, an artificial lake or reservoir is formed behind the dam. This can be used for flood control, drinking water, irrigation, recreation and industry.

Hydroelectric dams use the water to turn turbines which then generate electricity. 20% of the world's electrical energy is obtained via hydroelectric dams. There are consequences to the building of dams. Ecosystems can be destroyed. It has been estimated that 50,000,000 people around the world have been displaced by dam projects. Fertile sediments can get trapped by dams rather than running down the river and enriching the soil further. If a dam bursts, people along the river can get killed. In countries such as Brazil, India and China, dam developments are continuing. In the US, some dams are being removed.

Water pollution is the introduction of various agents such as chemical, physical or biological pollutants that degrade the water quality and harm the organisms that depend on the water as a habitat or for food. Their are two types of pollution.

Point Source Pollution

This type of pollution is where the pollutants are coming from a single source.

Nonpoint-Source Pollution

This type of pollution is where the pollutants come from many different sources. These sources can be difficult to identify.

If any land surface is polluted, the pollutants can get carried by rain into nearby stream, lakes and rivers. These pollutants can then enter into larger bodies of water as run off. As nonpoint pollution can enter into water from many different sources, they ca be difficult to pinpoint and regulate or control.


This is water that contains waste from residential homes or industrial plants. This water is treated before it's returned to lakes and river.

Sewage Sludge

The solid material that remains w=once the waste water has been cleaned is known as sewage sludge. This sludge often contains dangerous contaminants and is often incinerated before being buried in secure areas.

Thermal Pollution

Can you describe what has happened across each of these images?

How would you define thermal pollution?

Thermal pollution occurs when power plants and industries use water within their systems to col them down. The water is returned to rivers and streams at temperatures too high for the marine life to survive.

Groundwater Pollution

Groundwater pollution occurs when polluted surface water filters down into groundwater sources. Different types of groundwater pollutants include pesticides, herbicides, chemical fertilizers and petroleum products. Underground storage tanks are one of the biggest causes of groundwater pollution. The leaking of tanks is often due to the age of the tanks. Most underground storage tanks store fuel such as gasoline. You can also find underground storage tanks below farms and gas stations. Leakage results in the pollutants seeping into the soil and then into groundwater.


How would you interpret the images below...

Bio magnification is when the concentration of pollutants consumed at the bottom of a food chain accumulates as it works its way through the food chain to the predator at the top. Bio magnification can have significant implications.

Ocean Pollution

It's perfectly legal to dump waste products directly into ocean water. The majority of ocean pollution comes from activities that have taken place on land. This can be industrial, medical or toxic wastes that enter larger bodies of water such as oceans as run off.

Cleaning Up Water Pollution

In 1969 the Cuyahoga river in Cleveland literally caught fire due to the water being so polluted. This prompted the Clean Water Act of 1972. The purpose of the Clean Water Act was to "restore and maintain the chemical, physical and biological integrity of the nation's waters". The goal was to make all surface water clean enough for recreational activities such as fishing and swimming. As a result of the progress made following this act, the percentages of lakes and rivers clean enough for the activities identified hae increased by about 30%.

Other measures have also been adopted where. Stricter quality standards have been adopted where other toxic materials have to be removed from wastewater before it is discharged - this includes toxic metals.


Created with images by 44833 - "drop of water drop splash" • Mcability - "water glass drinking glass"

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