We use large amounts of water in our homes, workplaces and buildings. After we have used this water, it doesn’t just go away – it has to go somewhere. Some of it soaks into the ground, but much of it eventually ends up in a wastewater system, ranging from small on-site treatment systems (such as septic tanks and soil soakage fields), to very large sewerage systems and wastewater treatment plants.

Wastewater that contains human waste is known as sewage. The pipes that carry wastewater are known as ‘sewerage’ pipes or sewers.

Other sources of wastewater include industry, food production and commercial buildings, which may produce a mix of chemical and biological waste.

Wastewater contains pathogens (bacteria, viruses, protozoa) from human waste, which can cause disease if people come into contact with it. The most common illnesses from wastewater are the various types of gastroenteritis (stomach bugs, vomiting and diarrhoea), but people can also get skin and respiratory (throat or chest) infections.

In developed countries, keeping people and wastewater separate is normally very effective. However, there are situations where people can come into contact with wastewater. 

This most often occurs when wastewater overflows out of a sewer or wastewater pipe, usually because the pipes are blocked or overloaded during heavy rain. 

In areas without piped sewage systems, some form of on-site wastewater disposal is used. Septic tanks are the best known variety, and are common in rural parts of our region.


Pipe blockages

Pipes can get blocked by tree roots, debris such as wet wipes and disposable items, and cooking-fats and oils that solidify in the pipes. When sewers overflow in dry weather it is usually because of pipe blockages. Where these dry weather overflows occur depends on the site of the blockage. If the blockage is off of your property, the overflow will often be discharged into the street. If the blockage is on your property or downstream of your connection to the main sewer, the wastewater may back up into your toilet or onto your land through a ‘gully trap’.

Overflows onto people’s properties are often easy to see or smell. Animals and children can become contaminated, and track material into your house. Overflows to public areas such as parks, playgrounds, schools, early childhood education centres and houses can be of risk to public or environmental health.


Pipe overload in urban areas

During wet weather, urban areas served by ‘combined’ pipework (where the wastewater and stormwater pipes are combined in one pipe) overflow because of the volume of water in the pipes is too much for the size of the pipe. The water will then usually overflow at deliberately engineered overflow points, often in public places, and often into streams. In urban areas where the stormwater and wastewater pipes are separated, wet weather overflows can still occur due to inflow and infiltration into the pipes during wet weather, for example from illegal connections or broken pipes.


Wastewater overflows will often impact on wild food sources, especially filter-feeding shellfish. Avoid gathering shellfish from urban areas (where wastewater overflows are more likely), and where other contaminants are washed into the stormwater system, and then into the sea.


Wastewater overflows can contaminate streams, rivers, harbours, and the coast. This can make swimming risky. Auckland Council and Northland Regional Council operate the Safeswim programme to inform the public when it is likely to be unsafe to swim. Check Safeswim before you head out.

If you see a wastewater overflow on land, or in a stream or river, avoid it, keep children and pets away, and report it to:

  • Auckland Council on (09) 301 0101
  • Kaipara District Council on 0800 727 059
  • Whangārei District Council on 09 430 4200
  • Far North District Council on 0800 920 029

A pollution response team will clean it up.

If you have an overflow on your property, you can call a council Environmental Health Officer. However, if the blockage is on your property, the council may direct you to call a plumber or a drainlayer, and you will need to pay for the work yourself.

National Public Health Service - Northern Region provides public health advice to Auckland Council, Kaipara District Council, Whangārei District Council, Far North District Council and Watercare Services Ltd, and works with these organisations to reduce the number of overflows happening in our region. We strongly support Safeswim, which gives advice to the public about beaches to avoid that day.

Watercare Services Limited supplies water to Auckland and collects, treats and disposes of wastewater.

Last updated 19.3.2024

For health advice call Healthline for free anytime on 0800 611 116
MENU menu-arrow
health topics