Water hardness refers to the presence in water of calcium and magnesium, the origin of which is related to geological characteristics at the water’s source. Hard water, containing elevated levels of calcium and magnesium, causes difficulty in creating a soapy lather and forms crusty deposits (scale) in kettles,

electric irons and washing machines. If the scale collects on heating elements it shortens their life and makes appliances less efficient.

Auckland City’s water supply has very low hardness and therefore can be regarded as quite soft. For example, New Zealand drinking water guidelines state that total hardness (expressed as calcium carbonate – CaCO3) should not exceed 200 mg/L (milligrams per litre), whereas the average hardness level of water supplied from water treatment plants is approximately 42 mg/L.