All residents connected to a Tasman District Council water supply were urged to conserve water until further notice.
Four Civil Defence Centres have been opened to support those unable to return home, Nelson Tasman Civil Defence has confirmed.
Multiple roads are closed at the top of the South Island and will continue until further notice. This includes State Highway 6 Rocks Rd in Nelson, according to NZTA.
Flooding and slips also caused major disruption on roads across Northland overnight.