The UK Net Zero Carbon Buildings Standard Guide: Part 11: Carbon offsetting
The UK Net Zero Carbon Buildings Standard Guide: Part 5: Operational water use
Contributor
Hareth Pochee
MPhys
Principal Engineer
The pilot version of the UK Net Zero Carbon Buildings Standard (the Standard) was published in September 2024. The full document can be downloaded here.
The Standard has been produced by a range of industry professional organisations including RIBA (architecture), IStructE (structural engineering), CIBSE (services engineers) and RICS (surveyors), along with a large team of other industry organisations and professionals.
It aims to set out unambiguously, for a wide range of scenarios, the characteristics that buildings and building projects need to be aligned with the UK’s strategy to become net zero carbon by 2050. The Standard builds upon and supersedes previously published approaches such as the UKGBC Net Zero Carbon Building Framework, the RIBA Climate Challenge and the various LETI design guides.
Read more from our guide:
Part 1: Key principles and overview
Part 2: Embodied carbon
Part 3: Operational energy
Part 4: On-Site renewable generation
Part 5: Operational Water Use
Part 6: Fossil fuel free
Part 7: Electricity demand management
Part 8: District heating and cooling networks
Part 9: Space heating and cooling
Part 10: Refrigerants
Part 11: Carbon offsetting
Operational water use assessment and reporting requirements
The pilot version of the standard sets no limits for operational water use. However, it does require reporting and defines how this should be done. This applies to all water uses within the curtilage of the building (excluding manufacturing, production, waste of treatment or other industrial processes).
The standard requires the following operational water use metrics for assessment and reporting:
Reporting metric(s) name and unit
- Annual operational water use [m3/year]
- Annual operational water use per m2 GIA [m3/m2 GIA/year]
- Annual operational water use carbon emissions per m2 GIA [kgCO2e/m2 GIA/year]
Also:
- For Homes and Offices – Litres per person per day [l/person/day]
- For Schools – Annual operational water use per pupil per year [m3/pupil/year]
- For Data Centres – Water Use Effectiveness (WUE) [WUE]
Water use needs to be measured for each water source; network water supplier, ground water and other by taking meter readings (per source).
The carbon emissions from water use from all sources shall be calculated using the UK Government Conversion Factors for Company Reporting of Greenhouse Gas Emissions, full set (for advanced users) available at reporting period end point. The two relevant carbon emissions factors are: (1) the water supply carbon emissions factor and (2) the water treatment carbon emissions factor.
The standard requires assessment evidence and reporting for submission to the verifier to include (where applicable):
- Water use total and per source type breakdown in the relevant unit(s)
- Carbon emission factors used
- Meter readings and other water use measurement data
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Additional comments
A lot of water efficiency can be achieved through careful specification of sanitaryware however unless the project is being assessed, not enough scrutiny is applied to making sure that the right efficiency rates are achieved in practice. It is common for architects not to specify an efficiency, or for contractor’s to not consider the efficiency in any proposed swaps on site. The products and information are available but they often need to be sought out. The sticking point is often the flow rate used in showers. Our Passivhaus projects always specify 6l/min as an important part of reducing energy consumption. While lower flow than many people would desire, with a high-quality product this doesn’t have to feel like a compromise.
The use of rainwater or greywater harvesting were popular to include in projects years ago, however it was argued that costs and carbon to install and maintain these systems outweighed the benefits, therefore leading to the decision to not incorporate these into project designs anymore. As an industry we are accepting that these maintenance and costs burdens will need to be overcome due to the increasing concerns about low water levels and droughts in the UK, especially in dry areas such as Cambridge and the south of England.
Example from our projects
Ravelin Sports Centre, University of Portsmouth
Ravelin Sports Centre provides a range of facilities for both the University and the wider city, including a 25-metre swimming pool, an eight-court sports hall, a 175-station fitness suite, climbing facilities, a ski simulator, teaching facilities, and office spaces. Read the CIBSE Journal's article on the project, Keeping fit with less energy: Ravelin Sports Centre
We made analysis and mitigation measures to reduce water consumption as part of the design. The final design includes a pool cover to reduce evaporation and pool wastewater used for toilet flushing. The actual water consumption in use was analysed by taking weekly water meter readings over a year from 01/09/2022 to 31/08/2023:
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© Hufton + Crow
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Comments on the proposals
Aspects we think work well
Aspects recommended be considered for further development
For example, Part G of the Building Regulations (Appendix A):