Article written by: Alana Bowmar, Service Leader – Civil and Water Engineering and Jackson Turner – Graduate Civil Engineer
Wastewater collected from homes, businesses and industry is conveyed through a wastewater network to a treatment plant, where contaminants are removed before the treated liquid is returned to the environment. That return to the environment, whether to land or water, is known as a discharge and is the focus of the new Water Services (Wastewater Environmental Performance Standards) Regulations 2025.
There are over 330 wastewater networks across Aotearoa New Zealand, holding over 500 discharge consents (Taumata Arowai, 2026). Historically, these discharges were consented under the Resource Management Act 1991 (RMA) by regional councils and occasionally, the Environment Court.
Since the RMA was introduced, environmental outcomes have improved. However, the RMA process is resulting in inconsistent outcomes. A cursory look at the discharge consents around the country shows average limits for the main discharges are highly variable. Consent limits for key wastewater contaminants include:
- 5-day biochemical oxygen demand (BOD5) from 2 mg/L to 1300 mg/L,
- Total suspended solids (TSS) from 3 mg/L to 1200 mg/L, and
- Ammoniacal nitrogen from 0.5 mg/L to 50 mg/L.
There is no significant difference(1) between consent limits by discharge type (land, surface water, coastal waters), between population size, or date the consent was granted.
The reasons for these variances are complex. Long-term discharges have leveraged their historical environmental impacts, presenting minor treatment tweaks as improved environmental outcomes, where new discharges are held to a higher standard.
With no clear goal post, consent applications are treated as negotiations. Applicants who put forward wastewater management systems with little environmental impacts can be challenged just as much as those who put forward poorer systems – encouraging applicants to keep elements of the proposals “off the table” to bring forward through the negotiations.
This inconsistency results in significant uncertainty for applicants, making it difficult to forecast the costs associated with wastewater treatment upgrades. This also makes the consenting process long and expensive. There are examples where the cost of obtaining a wastewater discharge consent under the RMA is greater than the cost of the infrastructure to implement the same consent.
The Regulations were introduced to address these issues and represent one of the most significant changes to New Zealand’s wastewater consenting framework in decades. They are a positive and overdue reform. The new Regulations introduce nationally consistent performance requirements and provide much clearer direction on what is expected from municipal wastewater discharges.
For discharges to water, this consistency is largely achieved through treated wastewater quality limits, based on the dilution expected at the point of discharge. The result is greater certainty and a more transparent basis for infrastructure planning and investment.
Discharges to land present a different challenge. When wastewater is applied to land at appropriate rates, the soil, plant and animal systems have the capacity to retain a wide range of contaminants. These include organic matter, nutrients, biological contaminants, most heavy metals and many emerging contaminants. The land acts as part of the treatment process, requiring less investment in the treatment plant itself to achieve the same level of environmental protection.
However, this feature makes it more complex to set environmental standards. Effects resulting from land discharges are dependent on treatment provided by the site, which is dependent on the site-specific soils, topography, groundwater, climate, and land use. It is also dependent on loading rates: hydraulic loading and timing, nutrient loading and timing, and other contaminant loading rates. Impacts beyond the site are also dependent on the capacity of the environment to assimilate contaminants to levels that protect human and ecological health.
It would be possible, though challenging, to prescribe discharge to land standards comprehensively. Instead, the Regulations have taken a different approach. Part 4 of the Regulations establishes a framework for determining a Land Class based on Site Characteristics including soil drainage, soil texture, groundwater depth, slope, soil moisture conditions and nutrient uptake. These characteristics are then used to determine appropriate loading rates and management requirements through a site-specific Risk Assessment of specified public health and environmental effects.
This is a deliberate policy choice. Rather than prescribing every variable nationally, the Standards rely on classification and Risk Assessment to accommodate the diversity of Aotearoa New Zealand’s landscapes and wastewater schemes. The challenge is whether this standardised framework, which requires professional judgement, can deliver sufficiently consistent outcomes. If consistent outcomes cannot be achieved, will the Regulations encourage discharges to water over discharges to land, regardless of cultural and community aspirations.
As practitioners begin to apply the Regulations in real-world settings, it is becoming clear that implementation will not always be straightforward.
The Regulations introduce a high volume of technical and process terminology, much of which is not defined. As a result, significant questions arise that do not have clear answers, with experienced practitioners unsure of how they should be applied:
- What types of soils should meet the criteria “very well drained”, when New Zealand Soil Drainage classifications do not use this terminology.
- What constitutes a “minor” versus “extensive” drainage impediment?
- How should soils that do not meet any of the described soil texture categories, i.e., Pumice Soils, be classified.
- What density and volume of site-specific sampling is needed to inform a Land Class assessment? Over what time period?
- What level of analysis of modelling is required to support a Land Class assessment?
- What are the definitions of likelihood and consequence to be used in a Risk Assessment?
- What level of human health and environmental risk is acceptable?
These are not simply technical details. They directly influence the outcome of a Land Class assessment, allowable loading rates, infrastructure requirements and ultimately, affordability for communities. As a result, the consistent application of scientific and engineering judgement, paired with consistent expectations by regulators, remain central to achieving the outcomes sought by the Regulations.
Much of the real-world consistency will come from guidance, practitioner experience and early consent processes and case law. This creates both opportunity and risk. If interpreted too conservatively, land application schemes could become unnecessarily constrained, driving higher costs for councils and communities without proportional environmental benefit. If interpreted too liberally, public health and environmental protection may be compromised. If interpreted inconsistently, the confidence that the Regulations seek to create could quickly erode.
This is why the collaborative work to develop practical guidance, currently being undertaken between The New Zealand Land Treatment Collective (NZLTC) and Taumata Arowai, is so important. Vitruvius, through its involvement in the NZLTC, has been authoring some of this guidance.
Vitruvius have also recently undertaken a preliminary Land Class assessment on behalf of Taupō District Council for the Kinloch wastewater system, and we recently presented our findings at the NZLTC 2026 Conference, in Tauranga. Kinloch provides an interesting case study of applying the Regulations, as the wastewater system includes disposal via rapid infiltration beds at the treatment plant site, and slow-rate sub-surface irrigation on the Kinloch golf course fairways. Each of these systems follows a different Site Characterisation process, with the rapid infiltration having less characteristics to consider, and different category descriptions to apply.
The preliminary Land Class assessment identified that the existing sub-surface drip irrigation system on the golf course is constrained by localised hardpan layers, occasional winter saturation, and moderate nutrient uptake; despite the very high-quality treated wastewater from a membrane bioreactor plant. In contrast, the rapid infiltration trenches adjacent to the treatment plant were able to remove the hardpan layers during construction, and had less characteristics to assess, resulting in a more favourable preliminary Land Class assessment outcome.
This raised an important question: do historical operational priorities, which favoured subsurface drip irrigation over rapid infiltration, still make sense under the new Regulations?
Overall, the Water Services (Wastewater Environmental Performance Standards) Regulations 2025 have made significant progress towards creating greater consistency in wastewater management across New Zealand. However, for discharges to land they have intentionally stopped short of prescribing every factor that determines environmental performance. Instead, they rely on site classification and judgement to account for the complexity of natural systems.
The real measure of success will therefore not be whether the Regulations remove discretion, but whether they provide a framework within which that discretion is exercised consistently, transparently and proportionately. This will be achieved when practitioners assessing similar sites can reach similar conclusions, recognising genuine differences where they exist, and ensuring environmental and public health risks are appropriately managed. If this is achieved, the Regulations will have established a common basis to inform better infrastructure decisions; while balancing environmental protection, affordability and the realities of Aotearoa New Zealand’s landscape.
(1) Based on 95th percentile confidence intervals, using a Student’s T distribution.