Historically, Nelson has experienced wastewater overflows when heavy rain hits our region. This has resulted in wastewater getting into our waterways, which has a detrimental effect on our ecosystems. In some situations, overflows can result in popular swimming spots being closed off.

This isn’t a new issue and it’s not confined to Nelson. It is often referred to as inflow and infiltration, and is something that Council has been working to address.

We need your help. If you've noticed anywhere in your area where bad smells or noticeable overflows occur during heavy rainfall, then put a pin in the map below and let us know where to focus our efforts. We want to capture both new and historic issues, but in the case of an urgent issue please call Council on 03-546 0200 before using the map.

Inflow occurs when rainwater enters the wastewater system directly from the surface, typically through incorrect domestic plumbing; downpipes (spouting) incorrectly connected to wastewater pipes, stormwater pipes incorrectly connected to wastewater pipes, and damaged or low-lying gully traps or manholes. It can occur on both private and public properties.


When rainwater enters the wastewater system during a heavy storm it can result in sewage overflow onto private properties or the street, which then flows into our waterways.

Infiltration occurs when groundwater, ie. water that flows under the surface of the land, seeps into the wastewater system through cracks or bad joints in wastewater pipes and manholes. Similarly to inflow, this can cause sewage overflow during a heavy rainfall event and can also occur on private and public properties.

We have been working to reduce inflow and infiltration for some time.

We continue to inspect our own properties for any issues and fix them as needed. We also run an extensive programme of renewals and repairs to the wastewater network.

The current emphasis is on renewing earthenware pipes that are 80-100 years old and those that are in areas with high levels of groundwater. Targeting these pipes helps reduce the amount of groundwater that enters the pipes through cracks, joints and faulty manholes.


As a property owner, you play an important role in addressing this issue and helping to reduce the risk of overflows. If you find any issues that you can easily resolve, please take action now.

Please go outside your property and check these three things; downpipes, gully traps and sumps. Any problems you find related to these can be relatively inexpensive to fix, and if everyone made the effort we would see a marked improvement.

More information on what to look for can be found in our FAQ on Our Nelson.


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Do you know any spots that smell or overflow during heavy rain?

Put a pin in the map below to let us know where

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