Drinking water Flashcards
Fresh water comes from reservoirs, lakes, aquifers (underground rocks) and rivers, what is it likely to contain?
- objects like leaves and twigs
- insoluble solids such as particles of soil
- microbes, which may cause disease
The water must be treated to remove these.
What is the process of turning sea water into pure water called?
Desalination
Why do waste water and ground water need to be treated?
To make the water potable (safe to drink).
What does potable (drinkable) water have to have?
- low levels of contaminating substances
- low levels of microbes
Is tap water pure and why?
No, because it contains:
- dissolved salts
- dissolved chlorine
Name main stages in water treatment, and describe them.
1) sedimentation -large insoluble particles sink to the bottom of a tank.
2) filtration - small insoluble particles are removed by filtering through beds of sand.
3) chlorination - chlorine gas is bubbled from the water to kill microbes.
0) Screening - water is sieved.
What is the first stage?
sedimentation
What is the second stage?
filtration
What is the third stage?
chlorination
Why isn’t sea water drinkable and how is it made safe?
It contains too many dissolved salts to safely drink.
It can be made drinkable using simple distillation:
- filtered sea water is boiled
- The water vapour is cooled and condensed to form distilled water.
Distilled water does not contain dissolved salts, but it contains dissolved gases from the air.
What are the pros and cons of simple distillation of sea water?
- it uses a plentiful raw material
- produces pure water
- kills microbes in the sea water
- needs a lot of energy to heat the water/is inefficient and expensive
- not a suitable method for large volumes of drinking water
- It is carried out on a large scale so that resources are cheaper
Distillation is rarely used in the UK because of high fuel costs.
It is more suited to countries with low fuel costs, little fresh water, or plentiful sunshine to evaporate the water.
Name the stage before sedimentation.
Screening - water is sieved to remove large objects.
Explain why water used for a chemical analysis must not contain any dissolved salts.
Dissolved salts could react with the substance used in the analysis. A product formed in the reaction could interfere with the analysis, giving a false result. If the water used does not contain any dissolved salts, this will not happen.
Describe what is meant by ‘potable’.
Water that is safe to drink, drinkable.
In the UK, fresh water is piped from reservoirs so that it can be treated to make it safe to drink.
Name and describe the 3 main stages in water treatment.
(Screening - water is sieved to remove large objects)
Sedimentation - large insoluble particles are removed.
Filtration - water is filtered through beds of sand, removing small insoluble particles.
Chlorination - chlorine gas is bubbled through the water to kill microbes
