WaterNSW is undertaking a review of its Greater Sydney water supply system model, WATHNET and the system yield. The review will assess the model, modelling processes and assumptions used to estimate how much water Greater Sydney’s bulk water supply system can sustainably provide over the long term, while continuing to meet security and reliability standards.
What is WATHNET?
WaterNSW uses a computer model called WATHNET to assess the performance of Greater Sydney’s bulk water supply system and determine system yield.
WATHNET simulates the water supply system by representing:
- Dams and weirs
- Rivers and environmental releases
- Pipelines, canals, and pumping stations
- Water demands across the system.
The model uses over 100 years of historical inflow data to stochastically generate thousands of synthetic hydrology sequences. This allows the system to be tested against a wide range of extreme drought conditions that are worse than what has been experienced historically to ensure the estimated yield is robust.
What is system yield?
System yield is the average amount of water that can be supplied each year from Greater Sydney’s water supply system on a sustainable long term basis.
Yield is assessed against strict design criteria, that when met ensure:
- The risk of running out of water remains extremely low
- Water restrictions do not occur too often
- When restrictions are required, they do not last for extended periods.
Yield can change over time as the system changes, for example due to updated hydrology, refined modelling techniques, changes to infrastructure, or updates and revisions to system operating rules.
Why is WaterNSW reviewing the yield?
The WATHNET model and the system yield methodology are continuously improving and are independently reviewed in accordance with WaterNSW’s Operating Licence requirements.
WaterNSW also has new obligations to consider the impacts of climate change when assessing the Greater Sydney water supply system yield.
An independent expert reviewer has been engaged to assess the model, key assumptions, and methods used to determine system yield.
Contact the project team
Consultation is a key part of the process. WaterNSW is engaging with:
- Government and regulatory agencies
- Major customers and utilities
- Technical experts across industry and academia
- Other stakeholders with an interest in water supply planning and hydrology.
If you would like more information or are interest in participating in the WATHNET model and yield review, please contact the project team:
WATHNETReview2026@waternsw.com.au or contact the WaterNSW Customer Service Centre on 1300 662 077.
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