Australian Water Management Review Vol. 1 2014 | Page 98

There is much discussion in the ‘urban planning
space’ about how to make our cities more
sustainable with lower energy, water and ecological
footprints while maintaining the living standards
to which we have grown accustomed. In many
parts of Australia, harvesting rainwater from the
roofs of growing urban areas can meet 100% of
the annual demand of these new houses. Taking
this component of water away from the 10-fold
increase in runoff also reduces the adverse impact of
development on the local rivers and streams.

Developed by Wannon Water’s Peter Wilson,
regional roof water harvesting involves constructing
an independent roof water collection pipe network
within the subdivision in addition to the surface
water (stormwater) network. This collected roof water
can then be mixed with other raw water supplies
before treatment or be treated independently to meet
drinking water standards. Either way, it contributes
to the drinking water supply of the town or city.

NPC $/ML#

Ultimate yield per annum

Groundwater resource
development

$7.81m

$1,958

1500 ML

Regional Roof Water
Harvesting

$11.03m

$1,856

450 ML

Individual 5kL tanks

$8.53m ^

$5,482

210 ML*

The Toolkit

Estimates of the capital and operating costs
associated with the construction and operation of
the system are then calculated and a time-series
simulation is run to estimate the volume of water
harvested by the system annually.
(see Figure 1)
The toolkit’s cost estimates are primarily based
on data from the roof water harvesting system
92 | Australian water man age m e nt re v ie w

The Net Present Cost (NPC), which accounts for
operating and capital cost over the life of the project,
is lowest for roof water harvesting and less than half
the cost of individual tanks.

Notes:

Capital Cost

The toolkit developed by Wannon Water provides
water resource planners with a quick and easy way
to explore opportunities for roof water harvesting in
their region. It allows a roof water harvesting system
to be defined in terms of the collection system,
transfer pipelines, storage basins and a treatment
plant by entering a number of key parameters.

Cost/Benefit

In Warrnambool the project involves transferring
roof water to a water storage via a dedicated pipe

Water Resource Option Comparison
Option

to mix with other untreated water. It is then treated
through the existing water treatment plant to become
part of Warrnambool’s drinking water supply.

Figure 1. Schematic of Typical System

# The NPC is calculated over 34 years and divided
by the discounted volume of water over that period.
34 years to build out the catchment.
^ If applied to all 3280 houses in the catchment
* Assumes houses in the ultimate catchment (3280
houses) each have a tank yielding 70 kL per year on
average.