Napier City Council's wastewater system is overloaded and residents are being asked to only flush toilets or take baths if it is absolutely necessary.
The council says heavy rain has led to it asking for people to restrict household wastewater for 36 hours to "help get us back on track".
Residents are asked to keep showers short as well.
A statement on the council's Facebook page said:
"Our wastewater system has been overloaded by 24 hours of torrential rain.
"We're asking Napier to please keep their household wastewater to a minimum for the next 36 hours.
"Do not take baths or flush toilets unless absolutely necessary, keep showers short and leave the washing and dishes for another day.
"This will help us get back on track. Many thanks for your understanding."