There is growing support in the water sector for nature-based solutions (NBS) such as constructed wetlands, sustainable drainage systems and river restoration as opposed to the usual grey engineering solutions. They are often seen as a route for improving the water environment and increasing resilience in ways that are ostensibly more sustainable than traditional engineering solutions.

Central to this are their greenhouse gas emissions credentials - this is often mentioned, but quantified evidence is not always available. Indeed, there is likely to be a spectrum of outcomes, e.g. a) NBSs sequestering greenhouse gases over their lifetime; b) NBSs being net emitters, but significantly less than conventional solutions; or c) NBSs net emissions being similar to conventional solutions.

A gathered body of evidence on how to optimise the greenhouse gas emissions of NBS would therefore be timely and help with related decision-making and design.

The first phase of UKWIR’s research on process emissions from WWTWs suggested that they are currently underestimated, particularly in relation to nitrous oxide (N2O). Phase two is testing this through UK-based monitoring, and the accumulating evidence is that  process emissions are likely the largest part of water sector operational emissions.

We now need to gather evidence on the best methods for controlling nitrous oxide and methane emissions through modified operation of existing assets e.g. through real time monitoring and control, and repair and maintenance.

There is growing scrutiny of our embodied / scope 3 emissions: the quantum, our management of them. Inclusion in upcoming business plans and for England and Wales, in annual reporting.

A recent UKWIR project (ref: 22/CL/01/32 Calculating wholelife/ totex carbon) provided an appraisal of best / current practice, available tools​, and guidance on their systematic use. This built on UKWIR’s 2012 project (ref: 12/CL/01/15 A framework for accounting for embodied carbon in water industry assets) which included production of a meta-database of sources of carbon emission factors available from Government, academia, institutions and trade associations, water companies and suppliers.

We now need to update the 2012 work on construction carbon emission factors and pursue the areas for further research identified in the 2022 project. (ref: 12/CL/01/15 A framework for accounting for embodied  carbon in water industry assets).

Over the last 15 years the water sector has been developing tools for different aspects of its carbon footprint. Through UKWIR the Carbon Accounting Workbook provides a consistent approach for annual operational emissions. Also focused on operational emissions, the Water UK Net Zero routemap programme will culminate in the provision tools for estimating carbon reductions of different options over a given period of time, and the cost per tonne of CO2 avoided.

Now, growing attention is being paid to the embodied carbon of capital schemes and the sector’s supply chain. Already, various tools are available for estimating capital carbon emissions for new assets, (some of which include operational carbon) and with developments such as PAS2080 they are becoming more standardised. But uptake has been variable across the sector.

Two interconnected risks remain. Firstly, that embodied / capital carbon continues to receive less attention than operational emissions and that capital and operational carbon are not assessed in the round – contrary to totex thinking. Secondly, that the sector lags behind regulator and other stakeholder expectations on measuring capital carbon and building it into decision making and reporting

The organisations in the water sector of UK and the island of Ireland require common GHG estimation and reporting tools that can be used for annual accounting (FY 2023-24) and to report against the Ofwat Operational Greenhouse Gas emissions common Performance Commitment during AMP8 (2025-30).

Each year, companies within the UK water industry are required to report on their Greenhouse Gas (GHG) emissions to the industry Regulator. Companies also report on other aspects of their emissions to comply with other legalisation and regulations, such the Streamline Energy and Carbon Reporting (SECR) and climate related disclosures to keep stakeholders informed on emissions and transition plans. The emissions data also contributes to the net zero work that the sector is undertaking and progress of individual company emissions reduction commitments, pledges and targets.

UKWIR has developed a standardised workbook for estimating operational GHG emissions, the Carbon Accounting Workbook (CAW), to bring consistency and accuracy to the emissions estimation methodology used across the industry.  The workbook has been in place for 16 versions (up to 2022) and is updated annually to reflect latest UK Government emissions factors, evolving best practice and recognised international Standards for greenhouse gas emissions accounting and to incorporate changes in industry practices as well as outputs from relevant water sector research projects. This GHG estimation and reporting tools for 2024 project

This GHG estimation and reporting tools for 2024 project in addition to providing an updated CAW v18 to be used for annual accounting (FY 2023-24) will develop a parallel but separate calculation tool to be used to enable Water companies’ reporting to Ofwat against the AMP8 common Performance Commitment for Operational Greenhouse Gas emissions. This is a new performance commitment and therefore does not yet have a finalised scope or agreed calculation but will need a common methodology and supporting tool to ensure undemanding and consistent reporting is possible.

To avoid inconsistent greenhouse gas emissions reporting we need a common method and accounting system. This is achieved through the carbon accounting workbook (CAW).

The CAW requires annual updating - at the very least to incorporate revised emissions factors issued by BEIS. Previous updates have also included broadening the scope of items that are quantified, and improving functionality.