STORM and Water Sensitive Urban Design are closely related, but they serve different purposes within a Victorian development project.
WSUD is the broader design approach. It considers how stormwater, water reuse, infiltration, landscaping and drainage can be integrated across a development.
A STORM assessment is a quantitative treatment assessment. It measures how runoff from roofs, driveways, paving and other impervious areas is treated by nominated measures such as rainwater tanks, raingardens and permeable surfaces.
A STORM result may provide evidence that part of a WSUD strategy achieves the required stormwater-quality performance. It does not necessarily describe the complete water-management response for the site.
In practical terms, WSUD shapes the design, while the STORM assessment tests the treatment performance of selected parts of that design.
The terms STORM and WSUD are sometimes used as though they refer to the same report. This can create confusion during project scoping and council submissions.
They occupy different technical territories:
A project team may use WSUD principles to decide where rainwater tanks, raingardens, permeable surfaces and landscaped treatment areas should be located.
The STORM assessment then examines the runoff-generating catchments connected to those measures and calculates whether the proposed combination reaches the required treatment benchmark.
For a wider explanation of STORM reports and treatment assessments, visit the Certified Energy STORM Knowledge Hub.
A STORM assessment quantifies how effectively a proposed development treats stormwater runoff.
The assessment commonly considers:
The output is used to show whether the proposed treatment measures achieve the applicable stormwater-quality benchmark.
The assessment has a defined and limited purpose. It does not ordinarily provide a complete site-wide water strategy or detailed drainage design.
Water Sensitive Urban Design is an approach to planning and designing development so that water is managed as an integrated part of the site.
Depending on the project, a WSUD response may consider:
WSUD is therefore broader than a single calculator result.
It influences how the site is arranged and how water-management measures work together across architecture, landscape and engineering.
The simplest way to distinguish the two is to consider the question each one answers.
A STORM assessment asks:
Does the modelled combination of catchments and treatment measures achieve the required stormwater treatment performance?
A WSUD strategy asks:
How should water be managed and integrated across the development?
The STORM question is narrower and quantitative.
The WSUD question is broader and design-led. It may involve quantitative modelling, but it also considers site planning, physical integration, water use, landscaping, maintenance and coordination.
A STORM assessment can form one part of a broader WSUD response.
For example, the project team may develop a site strategy that:
The STORM assessment can test the treatment performance created by those measures.
It may confirm that the strategy reaches the relevant benchmark, or it may identify that additional treatment is needed.
The numerical result supports the design response, but it does not replace the need to show where the measures are located, how runoff reaches them and how they will be maintained.
The terms should not automatically be treated as interchangeable.
A STORM report usually documents:
A broader WSUD report may also address:
For a straightforward development, council may accept a concise stormwater treatment report and supporting plan information.
For a more complex project, a calculator output alone may not provide enough information to demonstrate the complete WSUD response.
Yes. A project can incorporate WSUD principles without necessarily requiring a STORM assessment.
For example, a development may include:
Whether quantitative treatment modelling is required depends on the planning controls, development type, application pathway and responsible authority.
Some projects may require another form of assessment, such as BlueFactor or MUSIC modelling. Others may demonstrate their water-sensitive response through plans, specifications and a planning report without a separate STORM output.
It may be possible for a project to achieve the required numerical result through a limited set of treatment measures.
For example, a large rainwater tank connected to a substantial roof catchment and regular reuse demand may produce a strong treatment result.
However, the calculator result may not answer broader design questions such as:
A successful numerical result should therefore be supported by a credible and coordinated physical design.
Several treatment measures associated with WSUD can contribute to the modelled STORM result.
Rainwater tanks capture runoff from connected roof areas. Their contribution depends on storage capacity, connected catchment and regular reuse demand.
Toilet flushing, laundry use where applicable, and landscape irrigation can help create storage capacity for later rainfall.
Raingardens can filter runoff from roofs, driveways and other impervious catchments.
The modelled benefit depends on the treatment area, catchment size and physical drainage connection.
Biofiltration systems use vegetation, engineered filter media and drainage components to remove pollutants from runoff.
They may form part of a landscaped treatment response for suitable projects.
Permeable paving allows water to pass through the surface and may support filtration, temporary storage or infiltration.
The area must be genuinely designed and specified as a permeable pavement system.
Suitable infiltration measures may reduce runoff and support treatment where site conditions permit.
Soil, groundwater, slope and building constraints may need to be considered before relying on infiltration.
Reducing conventional paving or replacing it with landscaping and permeable surfaces can reduce the amount of runoff requiring treatment.
Consider a three-townhouse development with:
The WSUD strategy may determine that:
The STORM assessment then measures:
In this example, WSUD provides the integrated site response. STORM tests whether the treatment components achieve the required performance.
The original Melbourne Water STORM Calculator has been replaced by BlueFactor for suitable small developments in Victoria.
This changes the current assessment tool but not the basic distinction between modelling and design strategy.
Older permit conditions and council correspondence may continue to request a STORM report or STORM score.
For a new submission, the project team should confirm whether council expects BlueFactor, MUSIC or another accepted assessment format.
MUSIC is another quantitative modelling tool, not a synonym for WSUD.
It can represent more complex catchments, drainage connections and treatment trains than a basic STORM-style assessment.
The relationship can be summarised as follows:
Both STORM-style assessments and MUSIC models may be used to provide quantitative evidence supporting a WSUD strategy.
Read STORM vs MUSIC: Which Assessment Does Your Project Need? for the dedicated modelling comparison.
Neither the term WSUD nor a STORM assessment should automatically be treated as a complete drainage design.
A drainage design may address:
A STORM assessment focuses on treatment performance.
A WSUD strategy may influence drainage design and landscape integration, but detailed hydraulic or civil documentation may still be required separately.
Understanding the distinction helps the project team commission the correct service and prepare the right documentation for council.
Confusing STORM and WSUD can lead to several problems:
A clear scope should identify whether the project needs:
Terms such as STORM report, WSUD response, stormwater treatment assessment and Stormwater Management Plan may imply different deliverables.
Establish whether the project should use BlueFactor, MUSIC or another method accepted by the relevant council.
The model should test treatment measures that can physically fit within the architectural and landscape design.
Roof, driveway and paved areas should only be assigned to treatment measures where the proposed drainage arrangement makes the connection achievable.
Rainwater tanks, raingardens and permeable paving used in the assessment should appear consistently in the project documents.
Treatment assets need practical access and ongoing maintenance. Numerical performance alone does not establish whether a measure will remain effective.
Confirm whether council also requires detention calculations, civil plans, discharge information or flood-related assessment.
A focused STORM or BlueFactor assessment may be appropriate where:
A broader WSUD response may be appropriate where:
Some developments require both: a WSUD strategy explaining the design and a quantitative assessment demonstrating its treatment performance.
Certified Energy can review the available plans and council correspondence to identify the stormwater treatment assessment required for a Victorian project.
For suitable developments, this may include:
The purpose of the assessment is to provide clear evidence of stormwater treatment performance without presenting it as a substitute for a broader water-management or drainage scope.
Explore the STORM Assessment Knowledge Hub or send through the current plans and council request for an initial project review.
WSUD is the broader approach used to integrate water management into the design of a development. STORM is a quantitative assessment used to measure the treatment performance of selected runoff catchments and measures.
A STORM assessment can support the stormwater treatment component of a WSUD response. It does not necessarily represent the complete WSUD strategy.
Not always. A STORM report usually focuses on areas, catchments, treatment inputs and the resulting performance score. A WSUD report may cover a broader integrated site response.
Yes. Whether a quantitative assessment is required depends on the project and council requirements. Another modelling method may also be used.
A project may achieve the numerical benchmark through selected measures, but the result should still be supported by a practical, coordinated and maintainable site design.
Rainwater tanks, raingardens, biofiltration, permeable paving and suitable infiltration measures may contribute where they are properly sized and connected to relevant runoff catchments.
No. BlueFactor is an assessment tool for suitable small developments. WSUD is the broader water-sensitive planning and design approach.
No. MUSIC is a modelling platform that can test more complex catchments and treatment trains. It may be used to support a WSUD strategy.
No. STORM addresses stormwater treatment performance. Drainage collection, pipe capacity, detention and discharge may require separate civil or hydraulic design.
Yes. The available plans, council request, planning controls and project complexity can be reviewed to identify whether a focused treatment assessment or a broader stormwater scope is appropriate.