Yesterday's deluge was not enough to halt calls for Aucklanders to conserve water.
Auckland Council's Watercare is encouraging residents to have shorter showers to help save water.
Storage dams in the Hūnua and Waitākere ranges have had about 40 percent less rainfall than normal this year.
Watercare spokesperson Roseline Klein said yesterday's heavy rain was helpful and demand had fallen, but more rain was needed.
"The rain we've had this week is forecast to be the only significant rainfall event of the month of July.
"It is helping - but it is not making up for the deficit we've got from the start of the year," she said.
Niwa scientist Chris Brandolino said Auckland, Hamilton, Whangārei, Whitianga and Kaitaia all had the driest first half of the year, with some places receiving less than half the normal amount of rain.
The second-half of the year is also expected to be drier than usual.
Ms Klein said having quicker showers and fixing leaky toilets could make a big difference to water supplies.
"If everyone in Auckland was to reduce their shower time by one minute - that would save 18 million litres of water every day," she said.