Work out your water supply emissions
= 75.5 kg CO2e in 2026 (Scope 3 (purchased goods and services)
Each m3 × 0.03776 kg CO2e, the Ministry for the Environment's 2026 figure (Water supply emission factors (m3)).
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Water and wastewater emission factors in the 2026 guide
| Factor (as the Ministry names it) | Unit | kg CO2e | CO2 | CH4 | N2O |
|---|---|---|---|---|---|
| Water supply emission factors (m3)Water Supply › Water Supply | per m3 | 0.03776 | 0.03654 | 0.001155 | 0.00005894 |
| Average for wastewater treatment plants (m3)Wastewater Treatment › Domestic Wastewater | per m3 of water supplied | 0.495 | 0.06287 | 0.2037 | 0.2284 |
| Average for wastewater treatment plants (per capita)Wastewater Treatment › Domestic Wastewater | per person | 45.68 | 5.802 | 18.8 | 21.08 |
| Septic tanksWastewater Treatment › Domestic Wastewater | per person | 175.2 | – | 149.9 | 25.3 |
CO2, CH4 and N2O are each gas's share of the total, in kg CO2e; a dash means the guide gives no figure for that gas. Every figure is from the 2026 guide; it is the only edition we hold, so there is no year-on-year column.
The Ministry's notes on these figures
- Water supply emission factors (m3): Based on energy related emissions.
- Average for wastewater treatment plants (m3): Part of the calculations are based on IPCC defaults.
- Average for wastewater treatment plants (per capita): Part of the calculations are based on IPCC defaults.
- Septic tanks: Part of the calculations are based on IPCC defaults.
- Uncertainty: The uncertainty for domestic and industrial wastewater methane and nitrous oxide emission factors are ±40% and ±90% respectively.
Worked example
Take an office using 2,000 m3 of water a year. 2,000 m3 × 0.03776 kg CO2e = 75.5 kg CO2e, reported as Scope 3 (purchased goods and services, waste).
How to use it
Multiply the cubic metres of water your sites used by the water supply factor. For wastewater, the guide's main factor is also per m3 of water supplied, so use the same volume again.
Where water is not metered, the guide gives wastewater per person (per capita). A site on a septic tank uses the septic tank row per person instead of the treatment plant factor. The water supply factor is based on the energy used to supply the water.
Water and wastewater are Scope 3. They are small next to energy and travel for most businesses, but customers asking for a full footprint often expect them.
Which rules apply in New Zealand
The Ministry's guide is voluntary guidance for organisations measuring their greenhouse gas emissions, and follows the GHG Protocol and ISO 14064-1. Climate reporting entities under New Zealand's climate-related disclosures regime report under the External Reporting Board's Aotearoa New Zealand Climate Standards, and can use these factors for their Scope 1, 2 and 3 figures. Businesses of any size answering a customer's or a bank's request for emissions data can use them in the same way. Cite the guide and its year next to every figure.
UK companies with sites or staff in New Zealand should use these factors for that activity and the UK government factors for UK activity. In Carbon Recycling, set a site's country to New Zealand and its electricity is reported with the Ministry's factor. See reporting overseas sites for how the rest fits together.
Where to find your own figure
Your water bill from the council or water supplier shows metered use in m3. Where water is charged through rates without a meter, use the per-person figures and the number of staff on site.
Related emission factors
- Waste to landfill (New Zealand): 0.6353 kg CO2e per kg
- Electricity (New Zealand): 0.07866 kg CO2e per kWh
- Natural gas (New Zealand): 0.1954 kg CO2e per kWh
- All New Zealand emission factors
- New Zealand grid electricity (Ember's estimate, every year since 2000)
- UK emission factors and other countries
Source: Ministry for the Environment. 2026. Measuring emissions: A guide for organisations: 2026 emission factors (version 2). Crown copyright, licensed under CC BY 4.0. Carbon Recycling is not affiliated with or endorsed by the Ministry; the sums on this page are ours.