The chance of Wellington experiencing an acute water shortage this summer has increased, while emergency water tanks sell out around the region.

New modelling from Wellington Water shows there is now a 33 percent chance of the region seeing an acute water shortage rather than a 24 percent chance that had been previously recorded.

Under that type of shortage, level 4 water restrictions would be brought into place which would ban all outdoor water use and reduce indoor water use by up to 50 percent.

Businesses would also have to significantly reduce their water usage.

Currently Wellington, Upper Hutt, Lower Hutt and Porirua are under level 1 water restrictions meaning that sprinklers can only be used every second day.

Wellington Water Regulatory Services director Charles Barker told RNZ the modelling was always being updated and used a number of different inputs.

"One of the things that has been recently incorporated is NIWA has released some updated forecasts and we've put that into the system and that amongst other things has lead to greater clarity there is a 33 percent chance of level 4."

The new modelling also showed there was a 70 percent chance of level 3 restrictions coming into force this summer, which would ban all outdoor residential water use.

Wellington Civil Defence is offering emergency 200 litre water tanks at a discounted rate around the region but they are selling out fast.

A Wellington City Council spokesperson said they had 80 of the tanks delivered today, but they all sold out by 12.30pm.

Currently both Hutt City Council and Upper Hutt City Council are sold out of the emergency items due to high demand.

Porirua City Council said it had a limited supply.