UPDATED 12.12PM Aucklanders have failed to save enough water and daily use is climbing well over the targeted amount.

And the Auckland Council has also revealed the culvert at the centre of serious flooding in New Lynn was on a "hotspot list" and inspected before the weekend's heavy rain that also led to water restrictions across the region.

Watercare today said the working week had got off to a bad start as Aucklanders used a whopping 419 million litres of water in the past 24 hours.

It warned the situation remained fragile.

If water use soared to last week's levels of around 460 million litres, partially treated water would be released into the network and a boil water notice issued.

Weekend savings met the daily target of 400 million litres of water or less and was tracking downward. Although it bucked the promising savings trend Watercare said yesterday's result was still lower than the previous Monday, when Auckland drained 464 million litres from the city's supply.

The Ardmore Water Treatment Plant was still working at half its usual capacity as it dealt with silt in the main catchment supply from the Hunua dams. Other water treatment plants at Waitakere, Huia and Onehunga were forced to work harder than normal to keep Aucklanders supplied with water.

Watercare is continuing to urge everyone to save 20 litres a person each day until the end of March.

In a briefing to the council's environment and community committee this morning, Watercare chief executive Raveen Jaduram said everyone was still getting safe drinking water.

He said the call for Aucklanders to save water resulted in use dropping below the target of 400 million litres a day to 390m litres on Saturday and 388m litres on Sunday.

"Yesterday at 419m litres, we still say 'thank you Auckland' but we request still for Auckland to keep reducing water.

"We don't want to ask Aucklanders to boil water. It will cause a lot of inconvenience," Jaduram said.

This morning, the council said Sunday's deluge significantly exceeded the design capacity of the failed Clark St culvert. This led to the culvert in the middle of New Lynn shops becoming "significantly blocked".

Experts were waiting for water level to drop to complete further investigations.

Another culvert behind a block of flats on Great North Rd, which was inundated, forcing all residents to evacuate, had also been flagged by council.

The council said the overland flowpath had caused the footpath to fall into the downstream waterway.

One commercial building had been red-stickered on Great North Rd and seven other premises have been issued with yellow stickers because of contamination and silt damage.

Nearly 30 people have been forced from their homes and need welfare support.