Aucklanders are being asked to reduce their water usage by 20 litres per day until the end of March, due to slips and erosion from the storm affecting the Ardmore Water Treatment Plant.
The plant is treating 50 per cent less water, as the water entering the plant contains a high level of silt which makes it a challenge to treat, according to Watercare.
Watercare chief executive Raveen Jaduram said they had to cut back on the volume of water being treated to maintain water quality.
"Luckily for Aucklanders, we are not reliant on a single water treatment plant," he said.
"Our metropolitan network has five treatment plants... and we’re running these as full capacity in order to meet our customers' needs.”
He expected it would take a few weeks for the silt to settle in the dams.
"There is no need to water the garden," he said.
Twenty litres is about two normal sized buckets of water.