1. 3 States
1.1. Solid
1.1.1. Ice
1.1.2. Snow
1.2. Liquid
1.2.1. Water
1.3. Gas
1.3.1. Steam
1.3.1.1. Cannot be seen
1.3.2. Water vapour
1.3.2.1. Cannot be seen
2. Water Cycle
2.1. Is the continuous movement of water from the Earth's surface into the air and back again
2.2. Involves the changes in the state of water through evaporation and condensation
2.3. Is important because it ensures that water on Earth will not run out and living things have a constant supply of freshwater
3. Processes
3.1. Heat gain
3.1.1. Melting
3.1.1.1. Water in the solid state (ice) gains heat to melt and turn into the liquid state (water)
3.1.1.1.1. Melting point of ice is 0 degrees celsius
3.1.1.1.2. When ice is melting into water, the temperature of the ice remains constant at 0 degrees celsius
3.1.1.1.3. Salt lowers the melting point of water to below 0 degrees celsius
3.1.2. Evaporation
3.1.2.1. Water in the liquid state gains heat to evaporate and turn into the gaseous state (water vapour)
3.1.2.1.1. Evaporation can take place at any temperature
3.1.2.1.2. Factors that affect the rate of evaporation include the presence of wind, the temperature of the water and the exposed surface of water
3.1.3. Boiling
3.1.3.1. Water gains heat at 100 degrees celsius and boils and turns into the gaseous state (steam)
3.1.3.1.1. Boiling takes place only at 100 degrees celsius
3.1.3.1.2. When water is boiling, the temperature of the water remains constant at 100 degrees celsius
3.2. Heat loss
3.2.1. Condensation
3.2.1.1. Water in the gaseous state (water vapour/steam) loses heat and condenses on cooler surfaces as water droplets
3.2.1.1.1. Sometimes, when water is boiling, steam condenses on the cooler surfaces of particles in the air and turn into water droplets which appear as mist
3.2.1.1.2. Water vapour loses heat in the Earth's atmosphere and condense on particles such as dust to form clouds
3.2.1.1.3. Why do our spectacles mist up after we leave an air conditioned room?
3.2.2. Freezing
3.2.2.1. Water in the liquid state loses heat and freezes at zero degrees celsius to turn into solid state (ice)
3.2.2.1.1. Freezing point of water is 0 degrees celsius
3.2.2.1.2. Salt lowers the freezing point of water to below 0 degrees celsius
4. Importance of Water
4.1. Water is essential to life
4.1.1. Without water, living things cannot survive
4.1.2. Water is needed by living things to carry out life processes such as transport and photosynthesis
4.1.2.1. Why do gardeners water the plants after adding fertilisers?
4.1.3. Many living things live in water such as in ponds, rivers, seas, lakes and oceans
4.1.4. A large part of living things is made up of water
4.1.4.1. What fraction of the human body is made up of water?
4.1.4.2. Where can we find water in a human body?
5. Water Pollution
5.1. Oil spills
5.1.1. Some fishermen and their families suffered from mercury poisoning when a factory polluted the water in the river. Why did they get poisoned even though they did not live on the river?
5.2. Litter thrown into water bodies
5.3. Poisonous wastes from factories
5.4. Untreated waste water from houses and buildings
5.5. Landslides
5.6. What can be done to discourage water pollution?
6. Water Conservation
6.1. Saving water and using it wisely
6.1.1. Controlling water pollution
6.1.1.1. Reducing pollution
6.1.1.2. Treating waste water
6.1.1.2.1. What is the purpose of the NEWater plant in Singapore?
6.1.2. Saving water
6.1.2.1. Installing water thimbles
6.1.2.2. Taking shorter showers
6.1.2.3. Using water-saving bags
6.1.2.4. Using half-flushes
6.1.2.5. How can you save water?
6.2. About 70% of the Earth's surface is covered with water but most of it is found in seas and oceans and is too salty to be drunk
6.2.1. Only 3% of water is freshwater that can be drunk