On-site wastewater systems, like septic tanks, treat domestic wastewater and return it to the environment inside the property boundaries.

Maintaining your septic tank is cheaper than fixing it and reduces risk to the environment.

A septic tank with a disposal field is the simplest and most basic wastewater treatment system. These systems tend to be older and consist of large tanks underground that collect wastewater from a dwelling on the property. They rely on good bacteria to break down your waste.

A septic tank separates wastewater into three layers:

Scum (e.g., paper and fat) — which floats on the surface.

Liquid — the middle layer

Sludge — which sink to the bottom of the tank

Septic tanks retain wastewater for long enough to settle solids to the bottom of the tank as sludge, while fats and oils float to the top.

The liquid is then slowly discharged to a nearby disposal field where it can soak into the ground.

The sludge remains in the tank and needs to be pumped out of your tank, along with any excess scum, roughly every three years. The timeframe depends on what you do to reduce water use and look after the good bacteria in your tank

This process is the same no matter what shape or size your tank is.

As a responsible tank owner, make sure you set a reminder to arrange the pumping of your septic tank with a local contractor.

Here are some handy tips to help keep your septic tank in good health

Reduce your water use:

• Only wash one full load of laundry a day
• Use washing machines and dishwashers only when you have a full load
• Use a front-loading washing machine to minimise water usage
• Install water-saving devices
• Fix leaky taps
• Take showers instead of baths
• Don’t put large volumes of water through your system (e.g. from spa pools).

Take care what goes down the drain:

• Scrape your dishes clean of food and fats before washing them
• Don’t put oils, fats or greases down your drain
• Don’t put coffee grounds down the sink
• Remove sand and soil from your clothes before washing them
• Don’t use a waste disposal unit
• Don’t flush sanitary products, disposable nappies, or ‘flushable’ wipes
• Don’t flush unwanted medicines
• Don’t put paints, weedkillers and other chemicals down the drain.

Use gentler cleaning products:

• Use detergents and cleaners compatible with your system
• Use biodegradable soaps and washing powder
• Don’t use strong bleaches, chlorine and disinfectants
• Use homemade cleaning products such as:
  • baking soda (for cleaning surfaces),
  • white vinegar (for cleaning tile grout with a toothbrush) or
  • lemon juice (one cup of juice in half a bucket of water instead of bleach).
  • see more below.
• If you do use harsher chemicals, please keep these to a minimum as they kill the good bacteria that breaks down your waste.

Know how your septic tank works:

• Get familiar with your septic system as good maintenance begins with understanding what type of system you have, how it works and where it’s located.
• Regularly inspect and maintain your septic system.
• Protect your septic tanks and disposal fields from vehicle access and large animals to avoid cracking the pipes and tank.
• Don’t allow stormwater into the disposal field.
• Don’t plant deep-rooting trees or shrubs over the disposal field and pipes
• Talk with a service provider about improving the system.

To ensure wastewater is properly processed, and to avoid odours and ponding, your septic tank and disposal field needs regular maintenance inspection and servicing by a qualified technician.

Polluting our waterways is not okay. It is therefore very important to maintain your septic tank.

Property owners are responsible for maintaining their septic tank, knowing how it works and having issues fixed as soon as possible.

The discharge of wastewater (whether treated or untreated) to water is contrary to tikaka (Māori custom and traditions). It means waterways can’t be used for customary practices, such as harvesting and eating mahika kai.

Taking care of your system is not complicated and does not need to be costly. Not taking care of your system can damage the environment and could end up being very expensive, especially if you have to replace the system. 

Septic systems have a lifespan of around 20 years. Regular maintenance and care of your system will keep it working effectively for many years to come.

Septic tanks rely on ‘good bacteria’ to break down some of the contents. Some sludge is needed in the bottom of the tank to support the good bacteria, but too much will reduce the amount of time the system can hold wastewater for. This means the wastewater cannot be treated properly, which could create an environmental problem.

Septic system failure occurs when your septic tank is no longer able to treat its contents. This happens when the good bacteria die off or your septic tank or disposal field is aged, damaged or too small for your family size or household use.

Signs to watch out for:

• Sinks, basins, toilets or showers are slow to drain 
• Sinks backing up when the toilet is flushed
• Fixtures make a gurgling noise when emptying
• A foul smell around your septic tank or disposal area 
• Abnormally high water level in your septic tank 
• Your septic tank is overflowing
• A gully trap or tank mushroom is overflowing
• Evidence of discharges around vents or gully traps
• The ground around your septic tank is soggy
• Puddles of (often smelly) standing water in or around your disposal field or where your septic tank is buried 
• Broken tank lids
• Pipe blockages 
• Scum and sludge build-up in your septic tank
• Black and slimy areas around your septic tank or disposal field
• Yellow or dead grass directly over your septic tank or disposal field in the cooler, wetter months.
• Lush green grass directly over your septic tank or disposal field during the dryer, hotter months.
• Algal blooms in nearby ponds or lakes

If your septic tank fails, you may need to have it pumped out and get a suitably qualified plumber or drain-layer to inspect your system. 

The following information should help you in preventing common problems. If you still have problems or questions, contact your specialist maintenance contractor

Avoid harm to the environment by keeping your septic tank and disposal field working well. If you are building a new system or upgrading, check the rules and consent requirements below.

You will need a resource consent if you cannot comply with the permitted activity standards – for example, your new system will discharge more than 2,000 litres per day, or effluent is going onto a neighbouring property.

Rules for on-site wastewater systems, including septic tanks, are covered in section 12.A of the Otago Water Plan.

• Rule 12.A.1.3 applies to systems installed before 28 February 1998.
• Rule 12.A.1.4 applies to systems installed after 28 February 1998.
• Rules 12.A.1.1 and 12.A.1.2 relate to long-drop toilets. 

If you notice problems with an on-site wastewater system (e.g., a septic tank) or pollution in your community, please contact:

• phone 24/7 pollution hotline on 800 800 033 
• email pollution@orc.govt.nz
• online orc.govt.nz/pollution

If you have any more questions, please contact us at:

• for consent-related questions consent.enquiries@orc.govt.nz
  for compliance-related questions compliance@orc.govt.nz