HOW LOW CAN IT GO? Texas Matiaha, Lower Hutt, at a depleted Hutt River with nephew Tehuritu Cooper, 6, and niece Lysigna Tam-Cooper, 1.

Twenty days of water is about all that's left for the people of Wellington, Hutt Valley and Porirua if the heavens do not open soon.

The dry weather has caused Greater Wellington Regional Council's bulk water supply to dwindle toward "crisis" levels, according to Nigel Wilson, who chairs the committee in charge of water supply.

The region has had no significant rain since February 4, while Wellington City has not had a drop for a month, MetService says.

INTERACTIVE MAP: The Big Dry

INTERACTIVE MAP: Water Restrictions

Almost all the available water in the region's rivers has been exhausted, prompting the council to activate an emergency consent yesterday, which allows it to take an additional 17 million litres or so each day from the Hutt River.

That will buy the council an extra 10 days before it has to tap into its emergency supply in the Stuart Macaskill storage lakes at Te Marua, north of Upper Hutt.

But because only one of those lakes was full at present, there would be only 10 days more after that before the 1900m-litre reserve was sucked dry, Mr Wilson said.

"So on day 21, we'll all be moving to Nelson or Hokitika for a drink of water."

Rain is forecast for Wellington and Wairarapa on Monday, and showers on Tuesday and Wednesday. However, a regional council spokesperson said the region needs at least two or three days of rain for the ground to soft up and moisture to be retained.

Wellington is not officially in drought. But when asked yesterday how far away that was, Mr Wilson was blunt.

"A couple more weeks and it's going to be all on . . . another three weeks and the cupboard will be bare."

Tapping into smaller reservoirs around the region was an option the council could look at after that.

On Saturday, councils in Porirua, Hutt Valley and Wellington introduced a ban on unattended garden sprinklers and irrigation systems but allowed watering by hand.

Those restrictions were likely to be tightened to a complete ban on hoses and sprinklers if two or three days of rain did not arrive in the coming week, Mr Wilson said.

Wellington City Council exempted itself from the sprinkler ban to water its sports fields and high-profile public parks.

But Mr Wilson said he hoped the city council would reconsider that position shortly.

"You go as far as you have to go with these [restrictions] . . . these are extraordinary circumstances, which nobody in living memory has ever faced before.

"Some of the measures might seem a little draconian, but this is a must-do situation."

A Wellington City Council spokesman said daily meetings were being held to work out where water use could be "dialled back".

The flow in the Hutt River is normally about 5000 litres a second at this time of year, but that dropped to 1300 litres last week.

The regional council can take water from the river till it reaches a minimum flow of 600 litres a second. But the emergency consent reduces that minimum to 400 litres, providing up to 17 million extra litres a day.

WHERE DOES OUR WATER COME FROM?

About two-thirds of the water supply for Wellington city, Porirua and Hutt Valley comes from the Hutt, Wainuiomata and Orongorongo rivers. The rest comes from Waiwhetu aquifer, a reservoir beneath Hutt Valley.

The regional council can take up to 150 million litres of water a day from Hutt River, provided a flow of at least 600 litres a second is maintained. A separate consent allows the council to take water until this flow hits 400 litres a second in emergency situations.

Wairarapa and the Kapiti Coast do not get their water from Greater Wellington Regional Council.

WHERE DOES IT GO?

Daily demand from about 380,000 people ranges from just over 100 million litres to about 180 million. The average this month has been 156 million litres.

Daily demand has peaked during summer dry spells at almost 220 million litres.

In recent years, the council has typically delivered just over a billion litres in an average week. If Westpac Stadium were a reservoir, this weekly volume would fill it.

The emergency consent was sought as a contingency should extremely dry weather occur while the council was enlarging and quake-strengthening the Stuart Macaskill lakes. One of the lakes, which would normally hold about 1500 million litres, is empty while this work is going on.

Mr Wilson said the council was monitoring the Hutt River and would stop taking additional water if it started to become a health issue for marine life.

MetService forecaster Brooke Lockhart said there was an increased chance of showers across the Wellington region for a few days from Sunday.

But the forecast was uncertain at this stage, because it depended on what path Tropical Cyclone Sandra took as it headed south towards the Tasman Sea.

Mr Wilson encouraged Wellingtonians to "be conscious, conserve, and we'll get through it all. The bottom line is, if you don't have to use it, then don't.

"People should shower with a friend, if that's an option . . . or put a brick in the toilet.

"If you know anyone who's particularly adept at rain dances, then encourage them to get out there and do what they do."

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