Treating water

Our processes start right at the source.

Auckland’s water comes from varied sources, including dams, bores, springs and rivers. Each treatment plant is designed to deal with its particular sources of raw water.

• The water from dams in the Hunua and Waitakere ranges comes from protected areas that are mostly native bush. It requires a relatively low level of treatment to meet the water standards. 

• Groundwater typically requires even less treatment, as the raw water is usually free from bacteria and has very low turbidity (cloudiness).

• Water from the Waikato River travels through a number of different environments on its journey to the water treatment plant at Tuakau, so it goes through additional treatment processes. 

Four plants treat Auckland’s dam water.

Most of Auckland's water comes from nine dams in the Hunua and Waitakere ranges. It is treated at four plants: Ardmore, Huia, Huia Village and Waitakere.

1. Screening

Water passes through screens that remove any large debris, such as leaves, branches, rubbish and dead insects.

2. Coagulation

To remove any dirt that remains, we typically add a compound known as aluminium sulphate (alum) to the water. The alum and dirt particles stick together (coagulate) into large, heavier particles called ‘flocs’.

3. Clarification

The water is pumped into settling tanks, or clarifiers, where most of the floc settles on the bottom of the tank and is removed. The clarified water is collected from the top of the tank.

4. Filtration

The water is forced through sand filters. These trap any remaining particles in the water.

5. Chlorine disinfection

Chlorine is added to kill any germs (micro-organisms), such as E. coli and campylobacter, which might remain after filtration.

6. Fluoride

Fluoride is added to the Auckland metropolitan water supply, with the exception of Onehunga. This is at the request of Auckland’s legacy councils (before Auckland Council integration). Fluoride is not added at rural treatment plants.

7. pH balancing

The final stage is to balance the pH of the water.

To maintain quality we take extra steps. 

This is because the water travels over 400 kilometres through towns and past farms and industries, before it reaches our treatment plant in Tuakau.  Runoff from farms and industries that use the water, such as power stations, affects the quality of the water before we treat it.

Our ultra-filtration process uses membrane technology: clarified water passes through fine membrane filters that prevent tiny micro-organisms such as giardia and cryptosporidium from passing though. This makes the Waikato treatment plant one of the most sophisticated in Australasia.