Lesson 4 – Storm-water Management in Natural Building

Why do we need to change our Storm-water Management practices?

Continued urbanisation and expansion has resulted in a dramatic increase in areas of hard and impervious surfaces, such as buildings, roads and car parks.

Consequently, the majority of the rain that falls in urban areas is converted into run off, or storm-water.

Traditional storm-water management practices direct storm-water into urban waterways, which carries pollutants that ultimately enter our rivers.

The increase in storm-water negatively affects the health and amenity of our waterways for people, plants and animals.

Additionally, the large volumes of storm-water entering our waterways can cause flooding that damages both natural and built environments.

How will best practice Storm-water Management benefit me?

Water Sensitive Urban Design (WSUD) can capture, treat and reuse storm-water onsite to dramatically improve the quality and quantity of water entering our waterways.

Integrating WSUD into your development will minimise its downstream impacts and also enables you to conserve potable (drinking) water by substituting it with rainwater.

WSUD strategies allow you to achieve the following outcomes and helps make the transition to a water sensitive cities:

  • Improve water quality in streams and in groundwater;
  • Protect stream and riparian habitats for native plants and animals;
  • Prevent erosion of banks along our waterways;
  • Reduce flooding risk;
  • Protect the scenic and recreational values of streams;
  • Conserve potable water by providing an alternative water source for uses such; as, irrigation and toilet flushing.


How does my choice of Storm-water Management strategies impact on the environment?

There is enormous scope for creativity when building or renovating to incorporate a variety of WSUD strategies into your design.

Some simple measures to eliminate the negative impacts of storm-water and conserve potable water are outlined below:

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Rainwater Tanks

Rainwater tanks are perhaps the easiest way to reduce the amount of storm-water leaving your property.

They also have the added benefit of providing a water source that can replace drinking (potable) water in certain uses such as outdoor use, toilet flushing and clothes washing.

By using storm-water to replace drinking water, savings of up to 90% can be achieved. Tanks come in many different colours, materials and designs.

They can be installed above ground, under ground, below outdoor decks, under buildings (if space allows), or even hidden within planter boxes.

Sizing rainwater tanks is contingent on a number of variables namely, rainfall, roof catchment area and proposed uses.

There are now a number of free tools, such as Tankulator and STORM, available to assist people in sizing their tanks and delivering best practice WSUD outcomes.

For more information on water tanks, see the resources section of this fact sheet and refer to the lesson on Water Efficiency.

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Porous Paving

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Porous paving allows rainwater to pass through the pavers and soak into the ground, unlike standard concrete or block pavers.


By using porous pavers you can:

  • Reduce the amount of ‘impervious’ surfaces on your block;
  • Increase groundwater recharge by allowing the water to soak through the soil;
  • Improve storm-water quality by filtering storm-water and reducing pollutant loads;
  • Reduce high flows during peak rain events entering the waterway from urban; areas causing stream erosion and habitat scouring.


Porous paving is installed in the same way as traditional paving and is available in many forms. They can be used to replace asphalt, concrete or other impervious pavers.


The average western family uses almost twenty percent of their drinking water in the garden.


Drought Tolerant Landscaping

You can not only reduce your water consumption by reusing household water or rainwater, but also by maintaining a water-efficient garden. T

his can be done through simple measures, such as using mulch, maintaining healthy soil or installing a more efficient watering system.

Drought tolerant plants are also an excellent way to save water in the garden.

They are better suited to our dry environment and create an attractive and low-maintenance garden.



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Installing a rain-garden on your property is an easy way to reduce pollutant loads in storm-water while providing attractive landscaping.

Rain-gardens are designed to capture, filter and reduce the flow rate of storm-water from roofs or hard surfaces.


“Generally, the size of the rain-garden should be approximately two percent of the run-off area. One square meter of rain-garden commonly treats 50 square meters of hard surface.”

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Measuring Storm-water Management Performance

To address and measure storm-water quality outcomes, the Best Practice Environmental Guidelines (BPEG) were developed.

These guidelines establish specific storm-water quality objectives, to assist in determining the level of storm-water management necessary.


The best practice performance objectives from the BPEG aim to remove:

  • 80% of suspended solids;
  • 45% of total Nitrogen;
  • 45% of total Phosphorus;
  • 0% of typical urban annual litter load.


For small and medium sized developments, Melbourne Water developed STORM, a free and simple online storm-water calculator that helps you assess and improve your design’s storm-water performance.

Exceeding the 100% benchmark in the STORM tool confirms that your building design will meet performance targets.

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