Results are in... 90% of Mr Gundry's students achieved a grade between A*-C! How'd you do? :)

C3 Water

← Back To Topics
Soft and Hard Water
Topic Quiz


Soft Water

When using soap, water can produce a rich, think lather.

Hard Water

Contains ions that reacte with soap to form scum.

Hard Water

Hard water forms because of magnesium and calcium ions dissolved in water. This happens when streams pass over rocks that contain compounds of these ions.

Gypsum - contains mainly calcium sulfate

Limestone - contains mainly calcium carbonate

Limestone does not dissolve in water very well, but can react with acid rain. When carbon dioxide dissolves in water it produces hydrogencarbonate ions which react with the calcium carbonate to produce calcium ions:

Wasting Soap

Hard water is unable to make a lather when using soap, at least until all of the magnesium and calcium ions have reacted.

As well as scum, hard water can often lead to (lime)scale forming. This is in an insoluble solid that can form when hard water is heated, leading to the break down of kettles, washing machines and other things.


  • Calcium ions help develop strong bones and teeth.
  • Some evidence suggests hard water helps reduce heart disease.


Water that can have its hardness removed by boiling/heating is known as temporary hard water.

Permanent hard water contains calcium/magnesium ions that are from salts such as sulfates. These cannot be removed by heating, but can be removed by other means.

Washing Soda

Sodium carbonate can be used to remove hardness as it 'traps' magnesium/calcium ions in insoluble carbonates.

Ion-exchange column

These columns are usually packed with sodium ions. These ions are exchanged for the calcium/magnesium in hard water.

Heating Hard Water


  1. When hydrogencarbonate ions are heated they decompose to make carbonate ions, water, and carbon dioxide gas.
  2. The carbonate ions then react with calcium/magnesium ions in the water.

Removing hardness in this way is very wasteful, as heating requires a lot of energy.

Water Treatment

Water for drinking should only contain low levels of substances dissolved in it, and hopefully low levels of microbes. It is made fit to drink by filtration methods that remove solids, and add chlorine/fluorine to remove those microbes. Water can be completely purified by distillation, but this is costly as it uses large amounts of energy.

Drinking water goes through several steps to be suitable to drink:

  1. Solids in the water must be removed by layers of sand and gravel
  2. The water is passed into a sedimentation tank, where aluminium sulfate is added to combine tiny particles to make larger particles, which are easier to remove.
  3. The water is then passed through a fine filter to remove very small particles.
  4. Chlorine is added to sterilise it by killing microbes.



  1. Some areas have had it for years and they're fine
  2. A study shows it causes a 30% reduction on teeth cavities
  3. It provides dental hygiene for those that don't visit the dentist regularly/brush their teeth
  4. Bacteria associated with heart disease are killed using fluoridation
  5. Fluoride is added in tiny amounts


  1. Fluorosis is a condition when you intake too much fluoride. It may weaken bones, and leaves white streaks on teeth.
  2. The benefit isn't that significant, is it worth the risk?
  3. It is ethically wrong to force people to drink fluorine
  4. Some studies show excess fluoride affects the brain, maybe even causes Alzheimer's
  5. There's no way to set a safe limit of fluoride, as you can't control how much water someone drinks

← Back To Topics
Soft and Hard Water
Back to top

Page last updated: 20/04/2017