Tough new measures are to be introduced in Tauranga to try and put a lid on the problem of sewage bubbling out onto some city streets during heavy rain.

Council has earmarked $180,000 to make a start on solving the huge problem of stormwater and groundwater entering city sewers.

City councillors heard that the point of no return for sewage overflows had already been reached five years before the planned completion of the $106 million Southern Pipeline.

Mayor Stuart Crosby said tens of millions of dollars were at stake and the council need to make its wastewater system as efficient as possible.

Council drainage manager Graham Dohnt reported that if it was only wastewater being flushed down sewers, then sewage popping out of manholes in the low points of the system would not start happening for another 10 years.

The problem of stormwater and groundwater infiltration was particularly bad in older parts of the city, he said. Causes included root penetration, cracks and breakages around manholes, and gully traps on private property routinely being used to drain stormwater.

Mr Dohnt said the problem was now so bad that about a quarter of the volume constantly carried in city sewers comprised groundwater leaking in.

Quantities increased markedly during storms, although he highlighted how even the recent fairly normal rain event on April 16 saw sewage overflow onto 3rd Ave and enter the estuary.

Council agreed to launch a $180,000 investigation to try and buy the city some more time by taking the top off peak flows down the sewers. It will include testing to identify the worst areas of intrusion and preparing a plan to remedy the problem.

If the investigation can be done quickly, council will consider spending a further $400,000 this year to start fixing cracked and holed sewers.

It also flagged that $1m a year could be spent over the next 10 years on the problem.

The other strategy was to crack down on householders who have illegally adapted their gully traps to alleviate minor surface flooding around their homes.

Mr Dohnt highlighted how reducing the intrusion would relieve pressure on the city's sewage treatment stationsputting off the day when expensive add-ons were needed to handle city growth.

The other big plus was relieving the strain on the city's wastewater pump stations and reducing power bills. Mr Dohnt added a caution that many councils had tried this, with some achieving nothing and others achieving an 80 per cent reduction.