Overview
ISO 20468-2:2019 provides a standardized methodology to evaluate the environmental performance of water reuse treatment systems based on greenhouse gas (GHG) emissions. The standard focuses on estimating types and sources of GHGs, selecting appropriate emission factors, applying global warming potential (GWP) conversions, and calculating a normalized performance metric - CO2‑equivalent (CO2eq) emission intensity - expressed as GHG emissions per unit volume of reclaimed water. Evaluations are limited to the operational phase of treatment systems (the period during which the plant is in service).
Key technical topics and requirements
- Principles: Guidance emphasizes relevance, completeness, consistency, accuracy and transparency when quantifying emissions.
- Boundary conditions: Defines what to include in the assessment (treatment system, residue management, auxiliary systems) to ensure comparable results.
- Stepwise calculation procedure (Clause 7):
- Step 1 - establish boundaries and evaluation scope
- Step 2 - calculate annual volume of reclaimed water
- Step 3 - quantify GHGs from energy consumption
- Step 4 - quantify biogenic emissions from biological treatment processes
- Step 5 - quantify emissions from consumables and waste generation
- Step 6 - account for GHG reductions enabled by resource recovery or reuse
- Step 7 - sum total GHG emissions
- Step 8 - compute CO2eq emission intensity (total CO2eq ÷ reclaimed water volume)
- Data choices: Guidance on selecting activity data, emission factors and calculation methods to ensure defensible results.
- Supporting material: Informative annexes include example emission factors, worksheets and sample CO2eq intensity calculations.
Practical applications and users
ISO 20468-2:2019 is used to:
- Benchmark and compare treatment technologies by CO2eq emission intensity
- Inform design decisions, process optimization and low‑carbon upgrades for water reuse plants
- Support environmental performance reporting, carbon accounting and sustainability planning
- Guide procurement, regulatory evaluation and lifecycle‑aware project appraisal
Primary users include water industry engineers, plant operators, environmental consultants, sustainability managers, regulators and researchers working on water reuse, carbon footprinting, and climate impact reduction for wastewater and water reclamation systems.
Related standards
- ISO 20468-1:2018 - General guidelines for performance evaluation of treatment technologies for water reuse systems
- ISO 20670 - Water reuse - Vocabulary (normative reference)
- ISO 14064‑1 - GHG accounting and reporting (relevant for aligning accounting practice)
Keywords: ISO 20468-2:2019, water reuse, greenhouse gas emissions, CO2eq emission intensity, emission factors, reclaimed water, treatment systems, environmental performance.