What is Calcium & Magnesium (Hardness)?

The two most common elements that contribute to water hardness are calcium and magnesium. When these precipitate from water they leave a white powdery precipitate that is often called lime scale.

The New Zealand drinking water standards give a guideline value of <200mg/L. However it is important to note that the drinking water standards are concerned with drinking water rather than plumbing. Issues around the home are noted at much lower levels.

The world health organisation recognises this and give the following descriptions:

<60mg.L Soft Water This means little or no lime scale found
60-120mg/L Moderately Hard Lime scale noted particularly where water is heated
120-180mg/L Hard Scale will form where hot or cold water comes into contact with fixtures
>180mh/L Very Hard Severe scaling expected

Where does hardness come from?

The hardness comes from limestone and sedimentary rocks which contain calcium and magnesium. As water passes these rocks, the calcium and magnesium dissolve into the water.

What does hardness/Limescale do?

Hardness means that water does not react with soaps and detergents as well as softener water. Soaps do not lather as well, they form an insoluble curd together and are the cause of ‘soap scum’. When showering in hard water it can leave the hair flat and skin feeling dull. When doing laundry, it can often feel hard or scratchy and colours can dull.

When hardness precipitates from water (it does this faster at higher temperatures), it leaves behind a soft white deposit, which is very similar to the limestone it came from. This is often noted as water spotting on glasses, shower doors, taps, showerheads.

The less noticeable issues are pipes slowly blocking reducing water flow, damage to dishwashers, washing machines, and hot water cylinders as hardness settles out in them.

Water heating is less efficient, as the hardness covers the elements, it essentially insulates them. THis means that the element has to work harder and harder to get the water to the same temperature.

Beware the imposter: It is important to note that another mineral, silica can cause the very similar-looking scale to hardness. However, removing it is very different. Click here if you want to test your water to see if scale is caused by hardness or Silica.

How can I remove hardness?

Water Softening is the most common, cost-effective method to remove hardness.