Stormwater harvesting could ease mains water demand

Council investigates diversifying its water sources

A decade of drought and extreme rainfall unpredictability has left councils across Australia in no doubt of the pressing need to plan for infrastructure to secure future water supply.

Dam storage levels in many communities dropped below 30% at the height of the drought. In response, many utilities are diversifying sources to reduce reliance on rainfall run-off stored in dams.

Gosford City Council has been investigating the feasibility of using harvested stormwater for non-potable water use to diversify its water sources.

Using eWater’s urban stormwater modelling software MUSIC (model for urban software improvements conceptualisation), a project team from the University of Technology, Sydney, assessed the viability of stormwater harvesting to supplement the existing water supply. Environmental and engineering consultants around Australia use this modelling software to design urban development proposals that meet water-sensitive urban design standards.

Applying MUSIC to the water balance modelling of the existing catchments allowed the researchers to determine the size of stormwater storage required to meet the projected demand.

Not a detailed design tool in itself, MUSIC rather aims to set out the alternatives for improving stormwater quality. The software is allowing planners to assess the pros and cons of various engineering systems for improving stormwater quality - biofilters, swales, wetlands and the like.

It includes major advances to the science and enhances the ability to model new stormwater technologies like porous pavements. It also includes raw rainfall data for 50 major population centres in Australia.

Gosford City Council is engaged in compiling year 2050 plans projecting expected growth and required infrastructure as a condition for receiving ongoing federal funding to help meet its responsibilities for supplying water to its residents.

The project shows harvested stormwater could reduce mains water consumption by up to 38%. However, further investigation will be required to determine the viability of implementing these stormwater harvesting schemes.

The researchers warn the current price of recycled water is too low for stormwater harvesting schemes to be financially competitive, meaning subsidisation may be required. They also suggested future investigations should focus on stormwater harvesting schemes for catchments of at least 30 hectares, in order to achieve the greatest economies of scale.

The results are playing a valuable role in helping the council with water recycling planning as it seeks to balance water demand and supply, while ensuring future water security. Being able to harvest stormwater for re-use would give the council an alternative water source to add to the mix.

There are many water uses which do not require potable water, including irrigation, toilet flushing and vehicle washing. Using water of lower quality like harvested stormwater could significantly reduce the demand on the mains water supply.