Parts of North Canterbury are facing septic tank overflow problems after heavy flooding.
A Waimakariri District Council spokesperson said Mandeville residents had been trying to drain their tanks simultaneously, which could potentially overload the council's sewer network.
There was also a risk the pumps could burn out, the spokesperson said.
Fifteen portaloos are being placed in affected areas.
Meanwhile, the Christchurch City Council is moving to reduce the amount of treated sewage being pumped into a local river.
The council plans to replace a pump station in Pages Road, to the north-east of the city, in a bid to reduce the level of treated wastewater being discharged into the Waimakariri.
More than 100 wastewater pumping stations and 528km of sewage pipes were damaged in the Canterbury earthquakes of 2010 and 2011.
Recent flooding has exacerbated problems, so flows from the Silver Fern Farms meat-processing plant at Belfast cannot be accepted when the network reaches capacity and are instead discharged into the Waimakariri River.