I'm a

Te kaha ōpapa o te wai

Water Hardness

Information about water hardness and how to reduce it at home

All of Auckland’s drinking water sources – dams, rivers, streams and underground aquifers – have different mineral compositions. This mineral content depends on the water’s journey from where it falls as rain to the place where we abstract it and treat it to make it safe to drink.

The mineral content of water stored in dams or abstracted from rivers is quite different from what we see in groundwater sources. Groundwater typically contains higher levels of naturally occurring minerals because of the path it takes through various layers of soil, rock and shell beds before it gets to our bores or wells, where it is extracted for treatment. The water picks up the minerals as it moves through the aquifer.

Minerals typically found in water include calcium, magnesium, sodium carbonates, silica, iron and manganese. The higher calcium, magnesium – and sometimes sodium – content means groundwater is often considered ‘harder’ than other drinking water sources.

About a third of the water used in New Zealand comes from groundwater sources.

Auckland’s groundwater sources fall in the ‘soft’ or ‘moderately hard’ category and are well within the recommended range stated in the New Zealand Drinking Water Standards. This range is based on guidance from the World Health Organisation.

While naturally occurring, these minerals can build up on domestic appliances and smooth surfaces in the form of ‘scale’. The scale may contain one or a combination of several compounds like calcium carbonate or silica. It may appear on shower doors and tapware, or in kettles and hot water systems.

Frequently asked questions

Can I reduce water hardness at home?
How can I reduce the formation of scale in my house?
How can I remove limescale?