Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions.
Give six possible causes of water emergencies, three due to natural causes and three due to humans.
Three possible natural causes of water emergencies: drought; flooding; earthquakes. Three possible causes of water emergencies due to humans: accidental contamination of the water supply (as in the Camelford incident); microbial contamination of water sources due to human mismanagement (such as the cholera outbreak in Haiti); deliberate poisoning of the water supply as an act of terrorism.
- What are the two treatment steps needed in household water treatment during a water emergency?
- For each of the two steps referred to above, suggest three possible options.
- What are the steps to follow if filtration cannot be undertaken and no water treatment chemicals are available?
- The two treatment steps needed in household water treatment during a water emergency are filtration and disinfection.
- Three options for filtration: cloth filtration, household sand filtration and ceramic filtration.
Three options for disinfection: boiling, solar disinfection and chlorination. (Other possibilities are the use of commercial products).
The solids in the water should be settled out and the water boiled before consumption.
Which of the following are not likely to require an emergency water treatment and supply system? Give your reason why in each case:
- A temporary camp housing people who have been displaced within their own country due to an earthquake.
- People who live in a residential area in a city.
- Refugees who have fled to cities in a neighbouring country due to fighting in their own.
- Refugees living in an uninhabited area of a neighbouring country.
The answer depends on the type and extent of the emergency but you may have identified the following groups of people.
- People who live in a residential area in a city – it is likely that a piped water system exists in such an area, so an emergency water treatment and supply system would not be needed.
- Refugees who have fled to cities in a neighbouring country due to fighting in their own – most cities will have piped water systems in place.
- List the stages of water treatment for an emergency water supply based on a water source where the level of suspended solids is high.
- How will the raw water be obtained?
- Name the coagulant and disinfection agents that are most commonly used in emergency water treatment.
- Why is the residual chlorine level in an emergency water supply raised to 1 mg l–1 about once a week?
- The stages of water treatment for an emergency water supply based on a water source where the level of suspended solids is high would be: addition of coagulant, sedimentation and chlorination.
- The raw water will be obtained from groundwater sources if available, as this will usually require only minimal treatment. The second option would be to use surface waters (for example, from a river or lake).
- The coagulant and disinfection agents that are most commonly used in emergency water treatment are aluminium sulphate and calcium hypochlorite, respectively.
- The residual chlorine level in an emergency water supply is raised to 1 mg l–1 once a week in order to disinfect the water containers used by the people served by the supply.