Watercare said the river usually provided about 20 per cent of the metropolitan water supply - or 125 million litres a day - but that level was being exceeded.
A spokesman said yesterday that Auckland's water supply was not affected by the present low river levels.
"This is because our plant is designed for very low flows. The intake is only 10 kilometres from the sea so it is always affected by the way tidal flows affect the river; and the normal tidal range is 600mm."
Most of the North Island could be declared a drought zone by the end of the week.
Droughts have been declared in Northland, Waikato, the Bay of Plenty and Hawkes Bay, with farming districts in Auckland covered by the Northland and Waikato droughts.
Wairarapa, Manawatu-Rangitikei, Taranaki and Gisborne have also asked for help as the dry spell continues.
Urban areas are also feeling the impact, with authorities in the Wellington region looking to draw water from the Hutt River as water reserves dwindle to only 20 days' supply.
Wellingtonians are being warned that if they continue to use excessive amounts of water, more restrictions will be put in place.
Greater Wellington Regional Council is being forced to take water from the Hutt River, as well as introducing a full outdoor water ban this weekend to cope with demand.
Water supply general manager Chris Laidlaw said residents should conserve the water they have.
"If we don't see demand coming down as much as we'd like to, then those restrictions will have to be a little bit more severe."
Mr Laidlaw said the council was hoping this weekend's expected rain will help ease the situation.
- NZ Herald with Newstalk ZB
