Should you count it?
For most offices and shops water is a small part of the footprint, but there are good reasons to include it:
- Wastewater is part of category 5. The GHG Protocol's category 5, waste generated in operations, covers wastewater as well as solid waste, and a PPN 006 Carbon Reduction Plan asks for category 5.
- The data is on a bill you already get. Metered water bills show cubic metres, so it takes minutes.
- Customers and questionnaires ask about water as an environmental issue in its own right. The government's environmental reporting guidance suggests reporting water use in cubic metres a year, and EcoVadis lists water as a separate issue under its Environment theme.
Mains water supply is optional for a Carbon Reduction Plan, because PPN 006 doesn't ask for category 1. Whatever you decide, say so in your method note.
The factors
| What | kg CO2e per m³ (2026) | Scope 3 category |
|---|---|---|
| Water supply | 0.1913 | 1, purchased goods and services |
| Wastewater treatment | 0.17088 | 5, waste generated in operations |
The government kept both factors the same as 2025 (water supply was 0.1913 in 2025 too). They are built from the carbon accounting workbooks UK water companies use for reporting to Ofwat, which include emissions from their offices and transport. The methodology notes that not every company's data was complete, so treat them as reasonable averages rather than precise figures for your area.
A worked example
A 25-person office uses 300 m³ of water a year. The bill doesn't show wastewater, so it is estimated at 95% of supply:
- Supply: 300 × 0.1913 = 57 kg CO2e
- Wastewater: 285 × 0.17088 = 49 kg CO2e
- Total: 106 kg, or 0.11 tonnes CO2e
That's about the same as 810 kWh of UK grid electricity at the 2026 factor. Real, but small next to the office's energy, travel and purchases.
Hot water is where the carbon is
The bigger effect of water use is the energy to heat it. Raising one cubic metre of water by 40°C takes about 47 kWh of heat before any boiler losses. From a gas boiler, that's at least 8.48 kg CO2e, around 23 times the 0.36 kg for supplying and treating the same cubic metre.
That energy is already in your gas or electricity, so don't count it twice. But it tells you where to act: spray taps, low-flow showers and fixing a dripping hot tap save far more carbon than the water figure alone suggests. If you run a kitchen, gym, laundry or care home, which all use a lot of hot water, it's worth a closer look. Our post on turning gas meter readings into kWh and CO2e helps you track it.
Things that trip people up
- Litres and cubic metres. Bills use m³. 1 m³ is 1,000 litres; entering litres as cubic metres overstates by a thousand times.
- Using spend instead of volume. The cubic metres on the bill give a better figure than multiplying the bill's cost by a spend factor.
- Shared buildings. If your landlord pays the water bill, ask for your share or estimate it by floor area or headcount, and say which.
- Counting wastewater twice. Report it once, in category 5, alongside your other waste.
How Carbon Recycling helps
In Carbon Recycling you enter water supply and wastewater from your bills in cubic metres. It applies the right year's government factor to each, puts supply in category 1 and wastewater in category 5, and if your bill doesn't show wastewater it suggests 95% of supply. If you also import your purchase ledger, leave the water account out once you've entered the volumes, so it isn't counted twice. For the whole picture of what to measure, see our guide on how to calculate your business carbon footprint.