People in Auckland are being asked to reduce their water usage over the next three weeks after floods affected water treatment capacity at the city's largest water treatment plant.

Watercare made the announcement this afternoon, but stressed that this was not an enforced restriction.

Around half of Auckland's water comes from four water storage dams in the Hunua Ranges - where flash flooding took place after heavy rain yesterday.

Chief executive Raveen Jaduram said water was treated at the nearby Ardmore Water Treatment Plant before being distributed to homes and businesses in Pukekohe, South Auckland, and as far north as Waiwera.


"We need Aucklanders to reduce their water consumption by 20 litres per day over the coming weeks until the silt in the dams settle and we can resume normal production at our Ardmore plant,'' he said.

Because of yesterday's flash flooding, the Ardmore Water Treatment Plant was treating about 50 per cent less water than usual.

That was because much of the water now contained a lot of silt from slips - giving the water a muddy hue and therefore making it more difficult to treat.

It would take up until the end of the month before silt would settle in the dams, he said.

Auckland was not reliant on a single water treatment plant, with five treatment plants in place for the city's water treatment.

They included one in Waikato and another in Huia, which were both running at full capacity.

"Our focus is on ensuring our customers receive high-quality water that is safe to drink straight from the tap. We're achieving this at the moment.

"But we have had to cut back on the volume of water being treated at our largest plant in order to maintain this quality,'' Jaduram said.

"I would like to emphasise that we're not enforcing water restrictions - we're simply calling for voluntary savings following an extraordinary and unprecedented weather event in the Hunuas.''


• Cut your shower time by two minutes. Approx saving = 16L

• Turn off the tap when brushing your teeth. Approx saving = 4L

• Don't use your toilet to flush rubbish. Approx saving = 7L

• Only run your dishwasher when full

• Only run washing machine when full