The South West’s water supply has traditionally relied on dams. However, declining rainfall and reduced inflows over the past two decades have significantly affected surface water availability.

To maintain a reliable water supply, the scheme now primarily relies on groundwater from the region’s deepest aquifer, the Yarragadee aquifer, via a bore near Nannup. Since 2018, between 5% and 27% of the scheme’s water has come from local dams, depending on rainfall and inflow.

The Department of Water and Environmental Regulation’s (DWER) South West Groundwater Areas Allocation Plan (2009) set aside a 3GL Blackwood Yarragadee Public Water Reserve for public drinking water supply. Water Corporation is currently licensed to abstract up to 1.9 GL a year from this reserve via the Nannup bore.

The Department of Water and Environmental Regulation (DWER) is responsible for water resource management across the State. They determine how much water can be taken from groundwater and surface water resources, while safeguarding the sustainability of the resource and protecting the water dependent environment.

DWER has initiated steps towards a review of groundwater resources across the South West Groundwater Areas, including the Yarragadee aquifer, over the coming years.

The region has experienced a long-term decline in rainfall and streamflow, which means our dams receive less water than they used to. This drying climate puts increasing pressure on the scheme, especially during hotter and drier periods.

The region continues to experience growth, development and activity from local industry, all of which contribute to increasing water demand.

This means we must plan carefully and continue investing in secure and climate resilient water sources to support our communities now and into the future.

The Yarragadee aquifer is the South West's oldest and deepest aquifer that is used for water supply. It provides a robust supply, even in dry years because of its vast storage and limited connection to the surface environment and overlying aquifers in the area where we draw from. If you would like to know more about groundwater management and aquifers visit groundwater.

The Department of Water and Environmental Regulation's (SSWER) South West Groundwater Areas Allocation Plan (2009) set aside a 3GL Blackwood Yarragadee Public Water Reserve for public drinking water supply.

We applied to the Department of Water and Environmental Regulation to access additional water from the Public Water Reserve in the Yarragadee aquifer. As part of this application, we requested an increase to our groundwater license from 1.5 gigalitres per year to 1.9 gigalitres per year, with a storage trigger. Our application was approved in early 2026.

Our decision to apply for a groundwater license increase was informed by a comprehensive review of water source options for the Warren Blackwood Regional Water Supply Scheme. This review assessed a range of options to maintain a reliable water supply, considering factors such as environmental sustainability, climate resilience, reliability, safety, and cost.

Based on these assessments and a comprehensive hydrogeological study, we identified groundwater as the most viable option for the scheme's future supply. The study included the monitoring and an aquifer pumping test which took place in December 2023, indicating that the Yarragadee aquifer can support increased groundwater abstraction to support the scheme without negatively impacting groundwater-dependent ecosystems, including the Blackwood River. These findings were submitted to the Department of Water and Environmental Regulation (DWER) for assessment and validation.

To help manage our water supply effectively, we've proposed a storage trigger for 1 August each year. This means that on 1 August, we'll assess the amount of water stored in the scheme's dams.

• If storage levels are above the trigger value, we'll limit groundwater abstraction to our current allocation of 1.5 GL.

• If storage levels are below the trigger value, we may need to increase abstraction to up to 1.9 GL to maintain a secure water supply for our customers.

This timing was chosen as it allows us to assess storage levels before the water year begins on 1 October, giving us a clear picture of what's needed to support the scheme through the warmer months. This is illustrated in Figure 1.

Water is a precious resource and should be carefully managed and used. DWER is responsible for the allocation of water resources for the state, including the Yarragadee aquifer and the entire groundwater system in the South West.

As part of our planning, we carefully consider the environmental impact of any changes to groundwater abstraction. We rely in expert advice provided from hydrogeological assessments to ensure we do not negatively impact the environment and groundwater system. We coordinate this work in collaboration with DWER.

In recent years we undertook a comprehensive review of water source options to support the scheme, which was completed in early 2025. The review assessed a range of options to maintain a reliable water supply, considering factors such as environmental sustainability, climate resilience, reliability, safety, and cost.

Based on this review, we have identified Yarragadee aquifer groundwater as our preferred option for the scheme's water supply, supported by infrastructure upgrades and operations improvements.

The shortlisted water source options were:

1. More water from the existing Yarragadee aquifer bore near Nannup. This is the preferred option.
   
   
2. A small filtration water treatment plant for Manjimup Dam and/or Millstream Dam to treat water stored there for as long as the sources are viable. Due to changing conditions, we are not able to continue using these dams without treatment, as there are incompatible land uses within their catchments. This option was not preferred as it retains scheme dependence on inflow.
   
   
3. A small borefield (two to three bores) drawing shallow groundwater near Manjimup. Investigative drilling was completed in early 2021. This option may yield up to 0.15 GL/year. This option was not preferred as it is not supported by DWER.
   
   
4. A new Yarragadee bore at an alternative location where environmental impacts can be demonstrated to be acceptable if an increase in capacity is not able to be achieved from the existing Yarragadee bore. Although a site has not yet been determined for this option, it would likely be at least 20 km from the existing bore. This option was not preferred due to cost, and the environmental impacts (such as clearing) associated with a more distant bore.

To determine the preferred water source, we consider factors including:

• Water quality
• Drying climate patterns and rainfall/streamflow data
• Impacts on local ecosystems and flora and fauna habitats
• Aboriginal Heritage and Native Title rights
• Community feedback and impact on private landowners
• Water treatment requirements and amount of water needed
• Cost of supplying water to our customers, including building the required infrastructure