1. Hydrology
Junior Science

2. As a solvent water forms solutions with many different solutes.
Solutions are simply mixtures of materials, one of which is a liquid or a gas. The liquid or gas, also called a fluid because it is able to flow.
One of the most common solvents is water. All water found in natural sources on Earth, except in rain water or ice, is in the form of a solution – such as salt water in the oceans and mineral water in rivers, springs, water and lakes. Minerals from the surrounding rocks are eroded and dissolved into the water. 2 2 2

3. As a solvent water forms solutions with many different solutes.
A solution is made up of a solvent and a solute. A solvent is a substance such as water that is able to dissolve a solute. The solvent ‘pulls apart’ the bonds that hold the solute together and the solute particles diffuse (spread randomly by hitting into each other) throughout the solvent to create a solution. The solution is a mixture with evenly spread solvent and solute particles. These particles can be physically separated by evaporation.
Solute (salt)
Solvent (water)
Solution (saltwater) 3

4. There are problems involved in obtaining an adequate supply of pure water.
884 million people lack access to safe water supplies; approximately one in eight people
DRINK: The first step in establishing a pure water system is to remove contaminants from a water source, so that people can drink it.
WASH: The second step is basic health and hygiene education, which is essential to change behaviours and establish good hygiene habits.
WASTE: The final step of a pure water system is the appropriate management of human waste 4 4

5. Some substances are more soluble in water than others.
The process of combining the solute and the solvent can also be called dissolving the solute in the solvent. The ability to dissolve is called solubility. The complete dissolution of one liquid in another liquid is called miscibility. When the opposite occurs, the substances are called immiscible
immiscible: oil and water
miscible: vinegar and water 5 5

6. Water is important for life on Earth
Without water, there would be no life on Earth. Water is continually moving around, in the ocean, rain and rivers, but the amount of water on Earth is fixed. The water that exists on earth today is the same water that existed billions of years ago. On Earth and in the atmosphere the water is continually recycled, in a process known as the water cycle. This cycle is important to all species on Earth, including humans.
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7. We have a fixed amount of water on Earth that continuously changes into different states – Water cycle
Water on Earth is always changing. Its repeating changes make a cycle. As water goes through its cycle, it can be a solid (ice), a liquid (water), or a gas (water vapor). Ice can change to become water or water vapor. Water can change to become ice or water vapor. Water vapor can change to become ice or water.

8. The processes by which water in changed from one form into another
When water falls to the earth as precipitation (rain or snow), one of three things may happen to it:
1. it may return to the atmosphere;
2.it may soak into the ground; or
3.it may flow over the surface into a stream, lake, wetland or the ocean.
Evaporation from these water bodies and from the soil returns water to the atmosphere once again

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10. Water is stored on Earth in different forms
Precipitation (rain, snow) may fall on vegetation, mountains or human-made structures, before reaching the ground from where it either evaporates into the atmosphere again, or flows to the ground.
When water flows into the ground may be taken up by plant roots for use in photosynthesis. The excess water diffuses through the openings in the leaves; this process is called transpiration.
Water that is not taken up by plants soaks into the spaces between soil particles and forms groundwater. Large collections of groundwater are called aquifers, and these are sometimes tapped with wells for drinking or irrigation. 10

11. Water is stored on Earth in different forms
Only 3% of Earths water is fresh water. Over two thirds of the fresh water is locked up as polar ice and glaciers while the remaining third is mostly ground water. That leaves only 0.3% of all of the Earths fresh water stored as lakes, rivers and swamps. 11

12. Water conservation
One of the biggest issues relating to the water cycle is the supply of drinking water and irrigation water for growing food. Only 0.1% of all the total fresh water is accessible in lakes, rivers and shallow groundwater. The rest is locked up in polar ice sheets or deep underground, and is not available for drinking or irrigation.
Because such a limited amount of water is available we must ensure we use water conservation methods to sustainably make the best use of the water we have.

13. Water conservation
The amount of water that is required to feed, clothe, house and transport a person is known as their ‘water footprint’.
Food harvested straight from the ground such as fruit and vegetables have a smaller water footprint compared to meats and processed food.
Generally the more steps a product has to go through before it reaches the consumer, the larger the water footprint.
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14. The atmosphere is a layer of gases that surrounds the earth
The Earth's atmosphere is an extremely thin layer of gases surrounding the surface of the Earth reaching to the edge of space. The thickness of the atmosphere is about 100 kilometres. Gravity holds the atmosphere to the Earth's surface.
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15. The composition of gases that make up air and the atmosphere
The largest portion of gas that makes up the atmosphere is nitrogen – a vital ingredient in plant growth but only once it is changed into it’s ion form. Oxygen makes up just under a quarter of the atmosphere and it vital for life on Earth. Only a very tiny portion of the atmosphere is made up of Carbon dioxide – required by plants in the process of photosynthesis – but increasing amounts produced from human activity are causing the planet to heat up.

16. The structure of Earth’s atmosphere
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17. The atmosphere transports heat and water
Heat energy from the Sun travels to the Earth in waves. The atmosphere and clouds reflect some of the heat energy back out into space. The heat energy that reaches the Earths surface is responsible for heating the planet and creating the weather.
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18. The atmosphere filters out deadly ultraviolet radiation
The Earths atmosphere contains a layer of gas called ozone – this is a molecule made up of 3 oxygen atoms. The ozone layer prevents most of the ultraviolet (UV) radiation that is emitted from the sun along with heat and light energy. UV radiation can cause damage and mutations (such as cancer) in living organisms. 18

19. The suns heat drives the weather
Different levels of heat on the surface of earth from the Sun is the main cause of wind, along with the spin of the Earth.
The amount of heat input on any part of the Earth varies because of season, cloud cover, latitude, and surface type. Ocean surfaces heat and cool slowly, Land heats and cools quickly.
When one area heats up the air pressure rises, and the higher pressure air expands and tries to move into the cooler lower pressure areas. Warmed air also rises, while cooling air sinks. All this movement of air causes wind. 19

20. Differences in temperature and moisture (density) in the atmosphere create movement of air particles
Clouds are made of condensed water or ice. All air contains water vapour - in different amounts, called humidity.
Hot air rises and as it does it cools. Cooler air can no longer hold all of the water vapour it contains and some of it condenses to form (visible) cloud droplets or ice crystals. 20

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