Summary

In this Study Session, you have learned that:

• Water is continually moving around the Earth and continuously changing its form. The hydrological cycle maintains a balance between evaporation, precipitation, the transport of water vapour in the atmosphere from the sea to the land and run-off from land to sea.
• About two-thirds of the Earth's surface is covered with water. Of this, around 97.5% by volume is held in the oceans as salt water; only 2.5% is fresh water and only a very small fraction of this is accessible as a water source.
• Surface water, groundwater and rainwater are our main sources of water. The quantity, quality, and reliability of available water are the important factors considered when sourcing water.
• Fluorosis caused by fluoride in water is a well-known health problem.
  
• Selecting a water source for a community supply system requires careful consideration of a range of factors, such as water quantity and quality, technical requirements and socio-cultural considerations.
• Water sources can be depleted by over-extraction and can be contaminated by pollutants.
• Globally, the consumption of water is increasing due to the rising population and increased consumption per capita. Water use per capita in developing countries is far less than in industrialised countries.