Clean water or Pure water?
Clean, potable water contains low levels of
dissolved substances and micro-organisms.
Pure water contains only water which can
be achieved by distillation (requires large
amounts of energy and is expensive).
Making water fit to drink
Step 1 (Screening):
Water passes through a screen
which catches large objects
(leaves, twigs)
Step 2 (Settlement):
Sand and soil settle out
EXAM SECTION
Questions and
model answers
Step 3
(Flocculation):
Aluminium sulfate
is added. Metal
ions clump
together and sink
to the bottom.
The sludge is
collected &
dumped.
Step 4
(Filtration):
Water is
filtered
through fine
sand. Water
is now clear.
Mygcsescience.com
video
Step 5
(Chlorination):
Water filters at home
Filters contain carbon to reduce the level
of chlorine as it is toxic, an ion exchange
resin to soften the water and remove
metal ions, silver particles to discourage
bacterial growth.
Step 7 (Neutralisation):
Adding chlorine to water will
make it acidic. The pH of the
water is adjusted to 7 before
it is send to consumers.
Step 6 (Fluoridation):
Fluoride is added to protect teeth from
decay. Excess fluoride might lead to
fluorosis- a condition where teeth and
bones become brittle. Excess fluoride
might also affect the brain.
Chlorine is added
to kill bacteria in
the water.
Alternatives to
chlorine are
ozone or UV light.