If you’ve ever heard the term “Cesspit” thrown around in reference to drainage, building consents, or property maintenance in New Zealand, you’re not the only one left scratching your head about what it actually means. It’s one of those terms that gets thrown around a lot in infrastructure and property discussions, but isn’t always thoroughly explained.
So, what is a Cesspit? Is it like a septic tank? Should you have one on your property? And who takes care of it?
Whether you’re a homeowner in NZ, a contractor, or you’re just curious about how stormwater setups work in NZ, here’s what you need to know about Cesspits in a straight-talking, no-holds-barred way.
The Simple Definition
In New Zealand, a Cesspit is a component of a stormwater drain system. It’s basically a concrete or plastic hole dug below ground level that collects water, most often rainwater, and any debris that comes with it. You’ll commonly find them at the side of the road, on driveways, in car parks , or at the entrance to a building. They appear to be nothing more than ordinary metal grates on the surface, but beneath, they serve a very critical function.
The systems work by trapping water, holding on to physical pollutants and heavy sediment, for example, sand and leaves, and then releasing cleaner water through a stormwater system. Without them, clogged drains and flooding would simply be a matter of course after every heavy rain.
Cesspit vs Septic Tank, What Is The Difference?
The two can be easily confused, especially if you’re hearing both for the very first time. But Cesspits and septic tanks are totally different systems with totally different purposes.
Septic Tank A septic tank is a component of a rural or off-grid wastewater system. It contains wastewater and organic waste, divides solids and liquids, before the liquid is discharged to a soakage field or surface irrigation area.
A Cesspit, on the other hand, is for stormwater, not sewage. It processes rainwater that pours onto roofs, driveways, streets, and paved lots. It’s the first step toward keeping your pipes from getting blocked and water from pooling. It is intended to filter out grit, litter, and heavy particles from surface runoff before the water flows onto the council’s stormwater pipes or a private soak hole.
Where in NZ are Cesspits Located?
You’ve likely walked past hundreds of them without even knowing it. They are typical in developed areas with extensive paved surfaces, where water cannot infiltrate the ground.
You’ll frequently see Cesspits at the foot of sloping driveways, or in the low points of car parking areas, on the perimeter of commercial buildings, near loading docks, and alongside roads. They are also a feature of newer subdivisions and lifestyle blocks in which the management of surface water is a factor in obtaining building consent and avoiding problems with erosion.
In the majority of councils, stormwater provisions are there in place for the management of runoff. One common method is excavating outhouse-style pits, an affordable and low-maintenance way to make use of your waste.
How Does a Cesspit Work?
At the top is a grate or grill through which water runs in; beneath that is a chamber, often 500 to 1000mm deep, where the water is gathered up. Larger particles such as sand, grit, and leaves settle to the bottom of the chamber. Lighter debris hovers closer to the top.
Some Cesspits are fitted with what’s known as a “trap” or “dip” pipe, which functions somewhat like the U-bend in your sink. It prevents floating substances from flowing out, and can reduce bad smell inside the drain coming up through the hole. When the water inside the pit reaches a certain level, it drains through a pipe that is connected to either the property’s main stormwater system or a soak pit.
It’s a remarkably simple system that does a tough job well, capturing the worst of the debris before it clogs up somewhere else.
Who’s in Charge of Caring for It?
It all depends on where the Cesspit is.
If it’s on the road, footpath, or in a public carpark, your local council is normally responsible for it. Auckland Transport, Wellington Water, and other councils have specialist teams that inspect and clean public Cesspits regularly.
But if the Cesspit is on private property, your driveway, under your carport, next to your workshop, then you’re on the hook for it. That means clearing the grate when there’s a blockage, as well as having the pit professionally cleaned when it becomes filled with sediment.
Blocked or forgotten about Cesspits may cause water overflowing into garages, over driveways, or under homes. In more severe cases, they can overflow in storms and spill into streets, causing flooding and damaging nearby properties. That’s why councils often write maintenance provisions into building consents, and why many owners of homes (the majority, no doubt with help from local companies) get their Cesspits inspected and cleaned by local professionals once a year, or once every two years.
How Often Should You Empty a Cesspit?
There is no hard-and-fast rule because it depends on how much debris falls into the pit, how much surface it is draining, and how often it rains. In leafy areas or where there are gravel driveways, they also fill more quickly.
It is generally good practice to check your Cesspit every 6-12 months, so we’re extra vigilant for any funny smells or leaks, particularly before and after winter. If sediment is beginning to approach the outlet pipe, which is typically identified or at least visible through a flashlight, the time has come to have things cleaned.
Others put it off until they see water not draining well, but by then, it might be a little too late. Clearing away water during a rainy day can ruin driveways, wash away garden edges, and even cause minor flooding.
Generally, having a Cesspit cleaned requires a vacuum truck that sucks out the sludge and rinses the interior of the pit. It’s a relatively quick job, and typically doesn’t involve digging or extensive disruption.
Do All Homes in NZ Have Cesspits?
Not necessarily. Many homes in older suburbs have older stormwater systems or soak holes, particularly on sloping sections or those with gardens around them. But in the new-build and regulations-bound landscape of stormwater control, increasingly, Cesspits are required, most of all where paved or sealed areas are, so as not to be able, naturally, to absorb water.
If you’re building, renovating, or subdividing in Hamilton, Auckland, or any of the larger NZ regions, your architect or council will normally raise the requirement for trade waste during the design phase.
Final Thoughts
Cesspits are among the quiet but vital parts of New Zealand’s infrastructure. They’re easily overlooked until something goes wrong, but when they’re functioning as intended, they conserve property, keep blockages at bay, and ensure stormwater flows where it should.
So, if you are looking for ways to solve stormwater issues, planning a new build, or considering how to maintain or improve the drainage on your land, you might start by understanding how Cesspits work.
And if yours hasn’t been looked at in a while, or the grate’s starting to become clogged every time it rains, it might be time to bring in the experts and get things draining properly again.
