Which wastewater system is best for a sloping site?
A lightweight plastic wastewater system is often a good option for a sloping site, particularly where access makes delivering and lifting a heavy tank difficult. NaturalFlow, EconoTreat and BioPod all have plastic options, so the best choice depends on the treatment your property needs and how the treated water will be distributed into the land.
A slope can also help gravity move wastewater through parts of the system. But before you start picturing a completely power-free setup, your designer needs to check the actual levels and where the disposal field can go.
The good news is that having a sloping section gives you several options. The trick is finding the combination that works with your land.
Why is a plastic tank often a good choice?
On a sloping property, getting the tank into position can be a sizeable part of the job.
A narrow driveway, tight corners or a building platform tucked down a hillside can make access challenging. Heavy concrete tanks need suitable delivery and lifting access, which isn’t always straightforward.
Plastic tanks are lighter to transport and handle, which can make installation easier on difficult sites. They still need excavation equipment and correct installation, but their lower weight can give your installer more flexibility.
And choosing plastic doesn’t mean you’re limited to one treatment system. NaturalFlow, EconoTreat and BioPod all offer plastic options.
That means you can consider access and installation alongside treatment performance, rather than letting the driveway make the whole decision for you.
First, understand the two parts of your wastewater system
If you’re building rurally for the first time, it helps to know that the tank is only part of the setup.
Your property needs space for:
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The treatment system: This receives wastewater from your toilets, showers, kitchen and laundry and treats it.
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The disposal field: Also called the land application area, this distributes the treated wastewater into suitable soil through a designed network of pipes, beds or trenches.
On a sloping section, both need careful positioning. The tank must be somewhere it can be installed and serviced, while the disposal field needs ground that can safely receive the water.
Can the slope help you use less power?
Yes, where the layout allows gravity to move wastewater instead of a pump.
If the house sits above the treatment system, wastewater may flow downhill to it. If the disposal field is suitably positioned below that, gravity may help with the next stage too.
However, the overall slope of your section doesn’t tell the full story. Your designer needs to check the height differences and distances between each part of the system.
For example, the property might slope away beautifully from the house, but the only suitable soil for disposal could be further uphill. In that case, pumping may still be needed.
A pump can also be needed to distribute treated wastewater evenly through an irrigation field, even when that field is downhill.
Gravity is a useful advantage when the layout supports it, rather than something to assume from the view.
Which WaterFlow system should you choose?
With plastic options across NaturalFlow, EconoTreat and BioPod, the next question is what you need the treatment system to do.
Your designer will consider the required treatment level, household wastewater volume, disposal method and your preferences for power use and maintenance.
NaturalFlow: where the site suits natural treatment
NaturalFlow uses biological processes, including worms, to treat wastewater without electricity in the treatment process.
For a completely power-free installation, the suitable slope range is 7–15 degrees, and the layout and disposal method must also support gravity operation. Being within that range is a starting point, rather than a guarantee.
It’s worth exploring where those conditions line up, particularly for an off-grid home. Outside that setup, pumping may still be required.
EconoTreat: where advanced treatment suits the design
EconoTreat provides advanced secondary treatment, cleaning wastewater to a high standard before it goes to the disposal field.
Its plastic options can combine that treatment performance with easier handling on sites where access is challenging. It can be paired with a designed irrigation system to distribute treated wastewater across suitable land.
The reason to choose it is the treatment and overall design your property needs, rather than the slope alone.
BioPod: a compact option with lightweight construction
BioPod combines biological treatment with a compact plastic tank, making it another option to consider where space or installation access is limited.
It uses power for its operating equipment, including pumping treated wastewater to the disposal field. As with the other systems, its suitability depends on matching the treatment and disposal design to your property.
All three deserve consideration where appropriate. The site assessment helps narrow the choice.
How do you stop the water collecting at the bottom of the hill?
This is one of the main jobs of the disposal design.
The aim is to distribute treated wastewater across suitable soil in manageable amounts. Simply letting it find its own way downhill could overload the lower part of the field.
Depending on the site, your designer may use pressure-compensating drip irrigation. This uses specially designed outlets to help distribute similar amounts of water across the field despite changes in elevation.
The pipes can be arranged to work with the contours of the land, with the pressure and layout designed for the slope.
In everyday terms, you want the whole field doing its share of the work.
How to work out what suits your slope
Sloping sections are nothing new in New Zealand, and we’re used to working with them.
Send us your plans or get in touch for a free project review.
We’ll help you understand your options, where the system and disposal field could go, and what to consider before you build.
