When was your septic tank last checked?

Failing to ensure your septic tank is maintained could put your family’s health at risk.

It’s estimated there are about 34,000 onsite wastewater systems, often called septic tanks, across Canterbury. It’s a relatively high number when you consider Auckland, with nearly three times the population, has an estimated 46,000. 

The most common system for single households in Canterbury is a primary treatment tank and land application system (i.e. a bolder pit or trench), but there are also some newer secondary treatment systems. 

If these systems aren’t looked after properly there could be serious consequences. Faulty systems can contaminate the land on your property or even the drinking water supplies of your whole community. 

Is your onsite wastewater making you sick?

When it comes to health risks from onsite wastewater, prevention is key.

Resource Management Technical Lead Jessica Newlands warns that problems often begin when people don’t maintain their systems and the tank or gully trap overflows, causing ponding of wastewater on the land surface.

“There’s a heightened risk in areas where the ground has had ‘human interference’ such as landscaping, vehicle movements or the installation of children’s equipment.”  

Institute of Environmental Science and Research (ESR) Senior Groundwater Scientist Bronwyn Humphries agrees, pointing to anecdotal evidence linking seepage with children’s play areas.

“Kids might just assume it’s a muddy puddle, and not bother to tell their parents.

“There was a case in Canterbury where children had sustained gastro for two years before the family finally figured out the kids were playing in a waste disposal field near their playground. It can take people a long time to realise something is wrong.”

Onsite wastewater can also enter groundwater, from which much of Canterbury’s drinking water is sourced. Weather can exacerbate the issue; prolonged dry periods followed by heavy rainfall events can cause wastewater to rapidly infiltrate groundwater, significantly increasing the risk of contamination. 

Sucking out the sludge

In a bid to understand some of the key issues around onsite wastewater, ESR reached out to a sludge removal company and asked them to log their jobs for a week.

The predominant problem was people not routinely getting the sludge sucked out every three years, as recommended. Instead, some were waiting up to ten years to get it done. Jessica says this ‘flush and forget’ mentality is concerning. 

“For every year that you don’t look after your tank, you’re increasing the risk that something will go wrong.”

She also urges people to do their research when purchasing a property with an onsite wastewater system. 

“Often when a rural property changes hands, the new owners have no idea what sort of system they’re getting, where it is located, or when it was last serviced. Real estate agents and lawyers are not legally required to disclose the type of system and the service history, so the impetus is on the property owner to find out all they can about the tank – including whether a resource consent has lapsed.” 

Spotting the signs

Signs of potential problems could include water presenting at the surface and offensive odours – often a strong ammonia or sewage-type smell.

Throwing bleach or antimicrobial cleaning products down your toilet is a big no-no, as it kills off the ‘good’ microbes that help to break down the sludge. Jessica says you should only flush the three P’s: Pee, Poo and Paper.

“Other items can cause blockages and added maintenance costs. Wet wipes and sanitary items should be put in the rubbish.”

Bronwyn recommends carrying out a ‘stress test’ to check whether your tank and land discharge are coping.

This involves running an inside tap for an hour or two, to simulate the household’s daily water use.

“Ideally, you’d want to do it in summer, during dry conditions. This makes any surface ponding easy to spot.” 

Maintenance is key

Regardless of whether your onsite wastewater system is new or old, keeping it well maintained will help ensure any problems are caught early.

As Bronwyn points out, it all comes down to the property owner’s care and knowledge.

“You don’t want your family to get sick, nor do you want to be the cause of a community contamination event, such as if wastewater from your property contaminates a downgradient drinking water well. You also don’t want your system to fail to the point where a complete renewal is required, which may cost between $30,000-$40,000.

“Enteric (occurring in the intestines) illnesses stemming from drinking water supplies that are contaminated by wastewater can include norovirus, which may leave you unwell for several weeks. Longer illnesses are also possible, due to pathogenic organisms like Cryptosporidium and Giardia.

“The cost to people’s health and your bank account could be very significant if things go wrong. I’d encourage anyone who’s been putting off their tank maintenance to act now.” 

Key tips for managing wastewater

• Newer, secondary treatment systems require regular inspection and maintenance at least every 12 months, including sludge removal every three years. Older, primary treatment systems (septic tanks) – while not requiring an inspection – still need to have sludge pumped out around once every three years.
• Support the microbial community living in your onsite wastewater system by using low-phosphorous soaps and detergents. Be sure not to flush solids such as wet wipes, or aggressive chemicals such as caustic soda. Water NZ has more information on what you can and cannot flush, and other advice for taking care of your onsite wastewater system.
• Try and space out water use to avoid overloading the system – for example not running your washing machine and dishwasher at the same time.
• If you notice an issue – like a sewage overflow, murky or smelly puddles around your treatment system, or even a broken tank lid – you should get your system inspected immediately by a suitably qualified technician.
• Before purchasing property with an onsite wastewater management system, check with a lawyer or estate agent whether the system is consented, and how it’s been maintained.

Read our

guidance about wastewater, how it is treated and your responsibilities.