Eight wells supply water from the Waiwhetu aquifer, beneath Lower Hutt, to GWRC's Waterloo Water Treatment Plant, which was commissioned in 1981.
Waterloo has a maximum production capacity of 115 ML/d, but typically produces about 60 ML/d or roughly 40 percent of our total annual supply.
Water treated at Waterloo supplies Lower Hutt (apart from Manor Park and Stokes Valley, which are supplied from Te Marua) and, mixed with water from Wainuiomata, also supplies Wellington's business district and southern and eastern suburbs.
Waterloo treatment process:
- The treatment process at the Waiwhetu aquifer is slightly different than the rivers, as it is an underground zone of water-holding sand, gravel and boulders beneath the Hutt Valley. Water takes more than 12 months to pass through the aquifer to our wells and is naturally filtered while underground.
- Waterloo treatment plant draws water from eight bores located along the “Knights Road spine” collectively known as the Waterloo wellfield bores.
- Once the bores extract the water it is then pumped to an Ultra Violet (UV) treatment unit at Waterloo treatment plant*.
*The Drinking Water Standards NZ recognises three classes of microorganisms that may cause disease: bacteria, viruses, and protozoa. UV treatment manages the protozoa risk, and if delivered in a high enough does can also treat bacteria and viruses, whereas chlorine on its own only manages bacteriological and viral risks. A combination of both treatment measures provides a multiple barrier protection system. Chlorination of the water drawn from the Waiwhetu Aquifer began after E-coli were detected in the Waterloo wellfield bores in December 2016.
- Once the water had been treated by UV at Waterloo it is aerated to remove carbon dioxide and lime is added to adjust the pH and alkalinity of the water (this is because the water in the Wellington Region is 'soft' and the lime and carbon dioxide help reduce the corrosive effect of the water on pipes and fittings).
- Flouride and chlorine are then added. The amount of fluoride is measured and dosed to target a range from 0.7mg/L to 1.0mg/L. The amount of Chlorine is measured and dosed to target a minimum residual of 0.2 parts per million at the far end of our distribution system.
For more technical information on the treatment process download Greater Wellington Regional Council's PDF below.