Safe and reliable drinking water is vital to the health and prosperity of our region and its people. We are responsible for making sure that the water supplied to Lower Hutt, Porirua, Upper Hutt, Wellington and South Wairarapa is clean and safe to drink.

Water from our rivers and aquifers (natural underground reservoirs) can contain microbiological material and a variety of naturally occurring chemical elements, some of which can cause health problems.

We monitor the water supply to make sure that there are no bacteria, viruses or protozoa (such as cryptosporidium and giardia) present following our treatment processes, as they can cause water-borne disease. We also monitor the concentrations of a range of chemicals in our water, to ensure that there are no metals or other chemicals at levels that are considered unsafe.

The criteria for determining whether a water supply is safe are contained in the Ministry of Health's Drinking Water Standards for New Zealand. Our monitoring and testing of the water supply is designed to prove that we meet these standards.

The Ministry of Health's (MoH) Drinking Water Standards for New Zealand (DWSNZ) lists recommended maximum safe concentrations of all chemical elements present in New Zealand water supplies that are known to be potentially harmful. Our water treatment processes are designed to provide water with much lower concentrations of these chemical elements than the Standards allow.

Check out the detailed chemical analysis for water from the Te MaruaWaterlooWainuiomata and Gear Island water treatment plants. Values are compared with the maximum allowable value (MAV) for that element as contained in the DWSNZ.

Water supply grading

Quality standards for drinking water are set by the Ministry of Health (MoH), through the Drinking Water Standards for New Zealand. Each year the Ministry publishes a grading for every public water supply. Gradings are based on the drinking water standards and indicate how safe each water supply is from contamination. The MoH grading system has two parts:

1.  A grading for the source of water and the treatment plant ("A1" to "E").   Read more

Chemical analysis - Te Marua

The following table shows the mean values of chemical analysis of the water supply from the Te Marua Water Treatment Plant, from 1 July 2019 - 30 June 2020, compared with the maximum allowable value (MAV) or guideline value (GV) for each element as set out in the Drinking Water Standards New Zealand (DWSNZ). Notes (A) MAV denotes the maximum acceptable value to comply with the Drinking-water Standards.   Read more

Chemical analysis - Wainuiomata

The following table shows the mean values of chemical analysis of the water supply from the Wainuiomata Water Treatment Plant, from 1 July 2019 - 30 June 2020, compared with the maximum allowable value (MAV) or guideline value (GV) for each element as set out in the Drinking Water Standards New Zealand (DWSNZ). Notes: (A) MAV denotes the maximum acceptable value to comply with the Drinking-water Standards. (B) GV denotes the maximum guideline value in the Drinking Water Standards.   Read more

Chemical analysis - Waterloo

The following table shows the mean values of chemical analysis of the water supply from the Waterloo Water Treatment Plant, from 1 July 2019 - 30 June 2020, compared with the maximum allowable value (MAV) or guideline value (GV) for each element as set out in the Drinking Water Standards New Zealand (DWSNZ). Notes: (A) MAV denotes the maximum acceptable value to comply with the Drinking-water Standards.   Read more

Chemical analysis - Gear Island

The following table shows the mean values of chemical analysis of the water supply from the Gear Island Water Treatment Plant, from 1 July 2019 - 30 June 2020, compared with the maximum allowable value (MAV) or guideline value (GV) for each element as set out in the Drinking Water Standards New Zealand (DWSNZ). Notes: (A) MAV denotes the maximum acceptable value to comply with the Drinking-water Standards.   Read more

Fluoride

Is fluoride added to my water?If you live in the reticulated parts of Lower Hutt, Porirua, Upper Hutt or Wellington, then you almost certainly receive fluoridated water. Petone and Korokoro - supplied from Hutt City Council's Rahui reservoir - are the only areas within the four cities that receive unfluoridated water. This is because they have historically had an unfluoridated water supply and Hutt City Council asked that GWRC continues that arrangement following a public survey in 2000.   Read more

Chlorine

Is my water supply chlorinated?All the water that we supply to Wellington, Porirua, Lower Hutt and Upper Hutt is chlorinated. Why is water chlorinated?Chlorine is a disinfectant that kills water-borne bacteria and viruses that could cause diseases. The water treatment processes that we use are designed to remove these germs as well as protozoa (such as giardia and crypyosporidium) from the water supply, but disinfection of treated water with chlorine provides another level of protection for the public.   Read more

Hard or soft?

The water supplied to Upper Hutt, Lower Hutt, Porirua and Wellington by Wellington Water can be described as soft. Water with high calcium and magnesium content is characterised as hard, while water with less calcium and magnesium content is soft. The sum of all calcium and magnesium compounds in water results in the total hardness, measured in milligrams calcium cabonate per litre (CaCO3, mg/L) – 1mg/L equals one part per million, or 0. 01millimoles (mmol)/L.   Read more