Hard water and soft water explained

Water ‘hardness’ varies throughout the UK; in London and the south east it is the hardest, whilst it gets progressively softer as you travel north.

What causes hard water? Here’s the science:

Rainwater naturally contains carbonic acid, which is formed by the reaction between water and carbon dioxide in the atmosphere.

When it rains, the water falls over rocks and passes through layers of rock in the ground. Compounds from these rocks then dissolve into the water, and the hardness of the water will depend on which region in the UK this happens, as the rocks vary throughout.

Hard water contains dissolved compounds, usually calcium or magnesium, and carbonic acid in the rainwater reacts with this to produce soluble calcium hydrogencarbonate.

carbonic acid + calcium carbonate = calcium hydrogencarbonate

It’s the presence of calcium ions and magnesium ions in the water that makes it hard. Whilst soft water will readily form lather with soap, it’s more difficult to achieve with hard water, so more soap is needed.

Measuring water hardness

One way to measure the hardness in water is to conduct a titration test with a soap solution.

  1. Pour a set volume of water into a conical flask
  2. Use a pipette to add a soap solution to the water
  3. Swirl the contents to help it form a lather

You may need to add more soap to form the lather, but once it has worked, record how much was needed. The harder the water, the more soap is required.

Types of hardness

Temporary hard water can be softened through boiling. Permanent hard water stays hard, even when boiled.

You should be able to distinguish temporary hard water from permanent temporary water but another titration experiment can be carried out.

Is hard water bad?

There are a number of environmental, social and economic considerations to be taken into account when determining whether hard water is bad or not.

The benefits of hard water include:

  • improved taste of water
  • helps reduce heart disease
  • good for the development and maintenance of bones and teeth.

However, the drawbacks are:

  • more soap is needed to produce lather so it can become more expensive
  • the scum produced by hard water can spoil the appearance of kitchen appliances and bathroom suites
  • the efficiency of kettles and heating systems can be reduced if limescale coats the insides of pipes and boilers – this can increase running costs and can cause a breakdown if a blockage occurs.

Softening hard water

In areas with hard water, the damaging effects can far outweigh the positives, thus it may be beneficial for the water to be softened.

There are two effective ways to soften water: add sodium carbonate or use an ion exchange column.

Sodium carbonate, or washing soda, can remove temporary and permanent hardness in water. It works because the carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble precipitates.

calcium ions + sodium carbonate = calcium carbonate + sodium ions

As the water no longer contains dissolved calcium and magnesium ions, it will form lather with soap more easily. However, the calcium carbonate and magnesium carbonate do form limescale, which is not only unsightly, but it can also clog up your pipes and cause appliances to break.

This means that treating hard water with sodium carbonate is only suitable in certain circumstances, such as softening water for hand washing clothes.

Commercial water softeners will often use ion exchange resins instead. These substances are usually made into beads and packed into cylinders called ion exchange columns, which can be built into machines such as dishwashers, or plumbed into water systems to continuously soften the water.

The resin beads have sodium ions attached to them, and as the water passes through the column, the calcium and magnesium ions swap places with the sodium ions. The calcium and magnesium ions are left attached to the beads and the water leaving the column contains more sodium ions, thus the hard water softens.

Once the resin beads in an ion exchange become saturated, they must be regenerated by adding sodium chloride (salt). In doing this, the sodium chloride replaces the calcium and magnesium ions on the beads so the process can begin again.

As sodium is so cheap and widely available, ion exchanges are a convenient and cost-effective solution to water hardness problems.

If you’d like to speak to us about making your water system more efficient, get in touch today.

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