What does Aa grade mean?

​The grading system provides a measure of the Ministry of Health’s confidence in the safety of a community’s water supply. Grades range from A1 to E and consider each aspect of water supply including the water source, treatment processes and the quality and management of the supply network to assess the level of risk of contaminated water reaching the consumer.

Under the Ministry of Health’s grading system Hamilton and Temple View’s water is 'Aa' grade. This means both our water treatment (A) and distribution (a) have maintained one of the highest grades since the system started in the 1960s, with an extremely low level of risk of contamination. Hamilton also supplies and monitors four small supply zones that have not yet been graded.   

What do we test for?

Water quality and safety is monitored at the water treatment plant and in all six supply zones in compliance with the Drinking-water Standards for New Zealand 2005 (Revised 2008).

Parameters such as pH, turbidity and disinfection criteria are measured continuously at the water treatment plant to ensure treatment processes are operating well. The bacteriological quality of the water is also tested daily at sites throughout the Hamilton supply network.

Compliance data is submitted to the Waikato District Health Board Drinking Water Assessor through a national database to ensure an independent verification of this compliance. This information is then reported nationally by the Ministry of Health as part of the “Annual Review of Drinking Water Quality in New Zealand".​

Additional testing for chemicals of health significance or for those that can affect the aesthetic quality of water (taste, odour and appearance) is carried out regularly at the water treatment plant and in the reticulation network to provide additional assurance that Hamilton’s water quality remains high.

For more information on health standards related to drinking water in New Zealand or for the latest Annual Review of Drinking Water Quality in New Zealand Report see Drinking-water - Ministry of Health.

Is Hamilton's water soft or hard?

Water hardness is a measure of calcium and magnesium content in water and is expressed as an equivalent quantity of CaCO3. Hardness generally originates from rocks and soil and, along with alkalinity and pH, affects the physical properties of the water.

The majority of New Zealand waters are considered to be soft, with a total hardness of less than 75g/m3 as CaCO3. The total hardness of Hamilton’s water supply is around 40g/m3 as CaCO3.

Backflow prevention

Backflow is when there is an unplanned reversal of water direction. This can result in contaminants within plumbing systems being drawn into the public water supply system, affecting the quality of our drinking water.

Backflow can be prevented by installing backflow prevention devices such as one-way valves or air gaps which prevent contaminants entering the water supply.

Hamilton City Council monitors backflow risk and installs backflow protection devices in the water system where necessary. Hamilton property owners, particularly high risk commercial properties, also have responsibilities to prevent backflow. 

Run a mug

​​Due to the softness of many of New Zealand’s waters, most water supplies are classified as plumbosolvent.

Plumbosolvent water is capable of dissolving trace levels of heavy metals such as lead and copper out of some household plumbing and fittings. Regular consumption of water containing these metals can, over a long period of time, pose a health risk.

The Ministry of Health therefore recommends that each morning households run a mug of water from the drinking-water tap before use. Any metals that may have dissolved into the water as it sits in the household plumbing overnight are then flushed out in this first run of water.

Related pages

Managing our water

Find out about our water services, how to conserve water, and our partnership with iwi.

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Last updated 15 July 2022