Summary of Study Session 4

In Study Session 4, you have learned that:

1. 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.
2. 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.
3. 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.
4. Fluorosis caused by fluoride in water is a well-known health problem in Ethiopia. The highest concentrations of fluoride are found in waters from the Rift Valley zone.
5. Selecting a water source for a community supply system requires careful consideration of a range of factors, such aswater quantity and quality, technical requirements and socio-cultural considerations.
6. Water sources can be depleted by over-extraction and can be contaminated by pollutants.
7. 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.