The New Zealand Environmental Protection Agency (EPA) is responsible for managing water pollution on behalf of New Zealanders. The EPA oversees the management of water quality and quantity, including stormwater runoff, in rivers, lakes, estuaries and coastal waters. The EPA also oversees groundwater protection, including groundwater monitoring and management. Stormwater runoff is collected, treated and either returned to rivers, lakes and the ocean, or to groundwater (if it matches EPA water quality standards).
Stormwater runoff is the volume of water from precipitation that is discharged from developed areas including streets, parking lots, driveways, and rooftops. Stormwater runoff is typically picked up by local storm sewers and treated before being discharged into a waterbody, such as a lake or river.
Here is a super informative post that goes into more detail.
As previously stated, owners are responsible for maintaining their property so that runoff water does not enter the stormwater system without first passing through a designated stormwater drainage system. However, the property owner cannot be held liable for stormwater runoff that enters the stormwater system as a result of natural stormwater runoff, such as runoff from a large rainstorm.
Municipalities and local authorities
A concept that can be difficult for some to understand is that the private property owner is responsible for stormwater runoff that lands on their property. Stormwater runoff is rainwater and snowmelt that runs off of a property after a storm, and it’s collected by a drainage system (stormwater drainage system). These drainage systems are usually on public roadways and in public spaces. Stormwater runoff can contain pollutants such as oil, grease, bacteria, viruses and other chemicals. If runoff reaches water bodies, it can harm aquatic life and the environment, possibly causing health problems.
As most of us know, stormwater runoff is a major cause of water pollution in NZ and New Zealand’s rivers, lakes, and oceans. Stormwater runoff is water that flows over the surface of the earth during or after a rainfall, from the surface of your property to a sewer or drainage system. In New Zealand, stormwater drainage is the responsibility of the property owner. However, there are a few exceptions to this rule.
Who is responsible for stormwater runoff NZ? The State Highway Authority (SHA) is the legal owner and keeper of the State Highway network, including stormwater drains and sewerage systems. Councils are responsible for local drainage issues. The National Environmental Information Council (NEIC) is the national body that coordinates the collection and management of environmental information to support sound environmental decision-making for New Zealand.
In most cases, stormwater runoff is the responsibility of the property owner. In some cases, however, municipalities or other government authorities are responsible. For example, in a commercial property, the building owner is responsible for stormwater runoff from the property. If the property is located in a floodplain, the owner is responsible for stormwater runoff even if it only reaches the property by way of a drainage ditch. Other municipalities may require new developments to pay a stormwater management fee.
The responsibility for stormwater runoff management is shared between NZ authorities and property owners. Councils are responsible for sewage, stormwater and wastewater management within their area. Councils set stormwater drainage rates and manage stormwater runoff in their area.
There are two main responsibilities for stormwater runoff NZ: the property owner and the local council. The property owner is responsible for managing stormwater runoff on their property. This includes ensuring that stormwater runoff does not enter watercourses or stormwater ponds and that it does not overflow onto your neighbours’ properties or into the ocean. Stormwater runoff is also managed by local councils. Councils are responsible for stormwater runoff management on larger areas of land, such as parks, sports fields, roads and rivers.