Purifying water Flashcards
(21 cards)
What is water purification ?
The process of cleaning water to remove germs & harmful substances
Is water that looks clean always safe to drink? why / why not?
No
Because you can’t always see the contaminants (without a microscope)
eg. germs, viruses, parasites that can make you very ill
What is contaminated water ?
water that contains unsafe substances such as germs
Why do many people in South Africa have contaminated water? what do they need to do with this water before drinking?
Many people do not have access to clean water (eg. running water in their homes) and so have to collect water from rivers / water holes.
They must purify the water before using it
List the 6 processes for cleaning (purifying)
To remove visible contaminants:
- sieving
- filtering
- settling
- decanting
To remove germs:
- boiling
- adding chemicals
What does sieving do / not do when purifying water?
pour dirty through a sieve
removes substances like dirt & rock (smaller holes –> the smaller a substance has to be to get through the sieve –> cleaner water)
does not remove germs & viruses
What does filtering do / not do when purifying water?
pour dirty through a cloth over a container
separates bigger substances (like plants, gravel & sand) from water
does not remove germs & viruses
What does settling do / not do when purifying water? explain the process
does not remove germs & viruses
it separates solid substances from the water (but they stay in the same container)
How: leave the water to stand still for some time, heavier solid substances fall to the bottom of the container & liquid part floats to top. Longer time –> more settlings –> cleaner)
You can add crushed seeds to make it settle faster (the substances will cling to the crushed seeds & drop to the bottom faster)
Has to be followed by decanting
What does decanting do / not do when purifying water? explain the process
does not remove germs & viruses
it separates solid substances from the water, done after settling.
How: pour the liquid (by carefully tilting) from the top of the settled container into another container
What does boiling do / not do when purifying water? explain the process
kills the germs, parasites & small organisms in the water
doesn’t take out solid contaminants (therefore often does after sieving/filtering/settling & decanting)
must boil the water for a few minutes & leave to cool (takes time)
What does adding chemicals do / not do when purifying water? explain the process
kills the germs, parasites & small organisms in the water
Most common used is chlorine (need to add just the right amount)
Some people use purification tablets
doesn’t take out solid contaminants (therefore often does after sieving/filtering/settling & decanting)
What do you need to make a water filter?
plastic bottle
scissors
cotton wool
sand
charcoal
pebbles
gravel
small stones
What order do you put the materials in to a water filter?
- cotton wool
- sand
- charcoal
- pebbles
- gravel
- small stones
What is the purpose of the gravel, pebbles & small stones in a water filter?
they act as sieve to take out larger debris in the water
What is the purpose of charcoal in a water filter?
removes impurities by adsorbing them (the impurity molecules stick to the surface of the charcoal)
What is the purpose of the cotton wool in a water filter?
to filter out small particles that float in the water that are hard to see
Can / should you drink water that has been filtered with your homemade water filter? why?
No.
Could still contain germs/bacteria etc
Need to boil it first
How do municipalities purify water?
dirty water –> through metal screens –> spiraling funnel –> minerals added (soapy)
–> funnel removes small substances (stick to sides) –> container –> sludge settles (sludge sucked out later) –> air bubbled through water –> sand filters –> chlorine gas bubbled through –> clean water pumped into holding tanks
at regular intervals, chloramine is pumped into the water
What is chloramine and why is it used in water purification?
Chlorine + ammonia
used to kill germs in
because the chlorine is only effective for a short time
Why is chlorine gas bubbled through water during municipal water purification?
to kill germs in the water
