fact sheet: Hard Water
Hard water isn't water that's hard as rock. Instead, it's water
that contains dissolved substances called minerals. These minerals
contain the elements calcium or magnesium.
have hard water?
You'll know if you live in an area where the water is hard by looking
in your kettle. Unplug your kettle and take a look inside when it's
cold. If you can see lots of solid white material, often called
a fur, and your cup of tea sometimes has scum floating on it, then
you've got hard water.
water become hard?
called calcium hydrogencarbonate is the main cause of hard water.
It forms when rain falls on limestone
and chalk rocks. These rocks are made of calcium
carbonate, which is insoluble
in water. Because rain water contains carbon
dioxide, dissolved from the air, this makes it acidic.
The rain water reacts with the rocks to form calcium hydrogencarbonate
which is soluble.
This is the white solid that ends up in our kettles.
An equation for the reaction is:
water + carbon dioxide
+ calcium carbonate = calcium hydrogencarbonate
(l) + CO2 (g) + CaCO3
Although hard water can be a problem in our kettles and to our
water pipes, it is not dangerous to us. In fact, soft water is more
likely to contain harmful dissolved metals. In areas where soft
water is common, the water companies take precautions to control
the amount of dissolved metals in our water.
to investigate hard water for yourself.
Year 10 pupils finding out about water hardness
top of the page