Bulk water supply
The total water supply to Lower Hutt, Porirua, Upper Hutt and Wellington varies between 120 million litres to 220 million litres per day, with the highest demand occurring during summer (mainly due to garden watering).
The level of supply during a typical day also varies as demand for water usually peaks at around breakfast time and in the early evening. Greater Wellington increases the amount of water supplied prior to these peaks to ensure that all city reservoirs are topped up ready for the increased demand. This has the added benefit of using power at the off-peak rates.
There are several reasons why a treatment plant may not be supplying water at any stage. The river that the water is taken from may be too dirty to use (generally after a storm) or the river flows may be too low to allow for water to be taken. The plant may also be undergoing some maintenance.