The rain expected early next week will not be enough to solve all the problems of the prolonged dry spell, but it will set up Otago to benefit from the next rainfall, hydrologist Dave Stewart says.

No significant rain has fallen in Otago in more than a month and, as a result, river levels were falling, irrigation restrictions were in force and fire bans instituted.

Water-carrying companies were gearing up as domestic tank water levels ran low across the city, from Taieri Mouth to Long Beach and Otago Peninsula.

Foote Haulage dispatcher John Mason said yesterday the company transported about 65,000 litres of water from the town supply to those who relied on tank water.

He expected it to get busier given the number of inquiries staff were getting.

MetService meteorologist Dan Corbett said the approaching weather pattern was the best the country had seen in weeks in terms of expected rainfall.

The remnants of Cyclone Sandra approaching from the north, and a trough coming from the Tasman Sea, were expected to bring widespread rain across the country.

While the bulk would probably hit the West Coast, some would fall in Otago and Southland.

A ''cool, flicky southerly'' would hit the region on Monday and possibly last until Wednesday.

It was hoped it would bring 15mm-30mm of rain. That would be followed by another high later next week, but it was hoped the break in the weather would signal a change in weather patterns, he said.

''It'll take more than one system to break the drought,'' Mr Corbett said.

Mr Stewart agreed but said cyclones were unpredictable so there was still uncertainty about the amount of rain Otago would receive.

''As long as it's more than 5mm we'll start to get some benefit.

''It won't fix the problem but it'll ease it.''

Any rainfall above 5mm would mean the ground would better absorb any further rain, he said.

Rain was also needed to flush some of the rivers in which weeds had increased because of the drier weather.

Yesterday, three rivers, the Shag, Kakanui and Taieri, at Tiroiti, had dropped to low-level alerts with irrigation restrictions imposed. Dunedin City Council water production manager Gerard McCombie said the rivers and streams which provided the city with its water were dropping but the network was coping.

Residents were being asked to voluntarily conserve water by using hand-held hoses rather than sprinkler systems.

Reservoirs held about 12 days' supply.

''That's a reasonable margin of supply over demand.''

-rebecca.fox@odt.co.nz