7. Water Discharge and Reinjection

Extra hot water is disposed of by Discharge or Reinjection. The amount of each has changed over time.
Water being discharged to the Waikato River has physically eroded the cement, exposing the larger stones. This process has been accelerated by acids that are formed when Hydrogen sulfide gas dissolves in the condenser water - Image: Heurisko Ltd.
The pipeline in the foreground carries hot water that will be used to recharge underground water at the edges of the geothermal field. The ponds behind are part of a prawn industry made possible by the use of waste heat energy - Image: Heurisko Ltd.


  • Discharge is when water flows into the Waikato River.
  • Originally this was the only method used at Wairakei.
  • Now 60 000 tonnes per day is discharged into Waikato River


  • Reinjection is when hot water is pumped underground
  • This is done either inside or outside the geothermal system field
  • Reinjection began in 1978, twenty years after generation began
  • Reinjection tries to stop the pollution of the Waikato River by elements such as arsenic
  • Now 46 000 tonnes per day is reinjected