Water hardness and your dishwasher

We have very soft water in Coffs Harbour, so you should use the setting for softest water possible on your dishwasher

You do not need to add salts or any other softening agents to your dishwasher.

Rainwater in a rainwater tank is also soft because it has not been in contact with any rocks and soil and so does not contain many minerals.

What is Water Hardness?

Calcium and magnesium minerals occur naturally in drinking water because they are present in the rocks and soils of drinking water catchments. In areas where the rocks and soils are naturally high in calcium and magnesium minerals, the drinking water will be "hard".

The rocks and soils in the Orara and Nymboida River catchments supplying drinking water to Coffs Harbour are naturally low in minerals; therefore we have "soft" water.

A quick way to know if you have hard water is to test how soap lathers into foam and bubbles - you will find the lathering process quick and easy in soft water and more difficult in hard water.

Another indication of hard water is the build up of lime scale on water fixtures – particularly those that use hot water, such as kettles, hot water systems and dishwashers. Heating causes the minerals present in water to drop out and form scale deposits, so in hard water areas with high levels of minerals scaling can be significant. This scaling problem is why the manufacturer of your dishwasher is asking you to be aware of the hardness of your water supply because in hard water areas, adding conditioning agents may be required to soften the water to avoid scale build up inside the dishwasher which could potentially have adverse effects on dishwasher operation and maintenance.

Luckily, this is not something you really have to worry about with Coffs Harbours' naturally soft water.

Measuring Water Hardness

In Australia, the concentration of Calcium Carbonate (CaCO3) is measured to ascertain the water hardness, which is expressed in mg/L. The Australian Drinking Water Guidelines 2011 state that water with a CaCo3 level of:

  • less than 60 mg/L is soft but possibly corrosive
  • 60-200 mg/L is good quality
  • 200-500 mg/L causes increasing scaling problems
  • greater than 500 mg/L causes severe scaling

Coffs Harbour Water provides public updates on the quality of our drinking water(PDF, 345KB) - including water hardness in mg/L - on a monthly basis.

Different countries around the world use several different units of measurement in relation to water hardness so if your dishwasher is made in/for another country, the operating instructions could ask for your local water hardness in one of these formats:

  • millimoles per litre (mmol/L)
  • parts per million (ppm)
  • degree of General Hardness (dGH)
  • deutsche Harte or German degree (⁰dH)
  • grains per Gallon (gpg) – American
  • english degree (⁰e)
  • french degree (⁰f)

Rather than converting our mg/L result into whichever of the various formats listed above is required by your dishwasher (you can research how to do this on the internet if you would like), Coffs Harbour Water advises all residents to set dishwashers for the softest water possible. For most dishwasher programming, knowing that you do not need to add any salts or other conditioning agents will be adequate.

For further information regarding water hardness, please contact Coffs Harbour City Council on (02) 6648 4000.

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