Climate-proofing the urban water supply


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Researchers from the University of Melbourne have joined an international collaboration with Indian institutions to protect diminishing clean water supplies by harnessing new water sources that are currently only partially, or not at all, tapped.

Arguably one of the most vital engineering challenges of our times is to ensure water supplies are not dependent on climate.

The collaboration is part of an Indian Government initiative called SPARC, the Scheme for Promotion of Academic and Research Collaboration. Researchers in Australia and India are exploring using alternative sources of water for daily human consumption as well as for agricultural environmental needs, as part of the ‘Integrated Urban Water Management Systems in Australia and India’.

The University’s research team includes Associate Professor Meenakshi Arora, Professor Peter Scales, Dr Wenyan Wu and Dr Anthony Stickland. The group ran a workshop in 2019 at the Indian Institute of Technology in Kharagpur, to identify the synergies and challenges  Australia and India face in securing reliable water supplies for their cities. The work aims to identify and share the lessons across countries.

Associate Professor Arora, says the team is focused on developing smart, economically viable and socially acceptable engineering solutions to exploit additional water sources such as wastewater and stormwater, so that they are regarded as safe, secure and valued resource instead of a low-value waste.

The global reliance on rainfall, and its increasing variability in many regions is presenting a tremendous challenge. More intense rainfall events can lead to flooding, while shorter periods of rainfall can tip regions into drought conditions.

“Another problem is our use of drinking water for non-potable uses including toilet flushing, laundry and garden irrigation, which could be supplied with treated rainwater or wastewater instead,” Professor Arora says.

Shortage and pollution - a global problem

The collaboration reflects the universal problems of water shortage and water pollution.

India’s challenge is multifaceted; underdeveloped water infrastructure and population pressure, compounded by most of its rainfall being delivered in one hit during the three-month monsoon season. India also has limited capacity to treat its wastewater, resulting in partially treated wastewater discharging into rivers and the sea.

By contrast, Australia faces seasonal rainfall on a dry continent that is getting drier. Despite highly developed water infrastructure, retrofitting new fit-for-purpose water sources would be economically prohibitive. Stormwater alone does not provide water security during drought in Australia and the use of treated wastewater for non-potable applications requires the installation of a third pipe system.

“So, the challenges are different, as are the solutions and opportunities, which tend to be site specific, but the underlying problems are shared – water shortages and increasing water and waterways pollution,” Professor Arora explains.

The team is working with the Indian Institute of Technology at Kharagpur in West Bengal. The region has ageing infrastructure and experts estimate that half of its wastewater is leaking and contaminating groundwater. The area also suffers from an intermittent and rationed water supply.

Similarly, Australia is experiencing severe water shortages, primarily due to population growth and the impacts of climate change. River systems are stressed due to low flows and increasing pollution levels, country towns have been running dry, and drought even brought Melbourne to the brink of running out of water during the millennium drought.

“The solutions we are working on for both countries aim to diversify water supply – to stop relying on drinking water for all our water needs and instead make use of all available sources, accepting different water qualities for different purposes,” Professor Arora says.

“This would preserve fresh, clean water for drinking and personal use, and utilise alternative sources for toilets, laundering, gardens, etc. We have calculated that 40 per cent of drinking water could be saved if we use alternative water sources for non-potable uses.”

Protecting water security in times of drought

Professor Arora says alternative sources include domestic rainwater tanks that provide ready-to-use water, and stormwater that can be captured, treated and stored for later use. However, for tanks and stormwater to be viable, we still need rain. For security against droughts, we need sources that are not dependent on climate.

“The two main options are desalinated sea water and treated wastewater, although the former is only appropriate for coastal communities. And while cities generate wastewater every day, regardless of climate, this wastewater often only gets treated to a level suitable for release into the environment, not for reuse by people.”

The introduction of a third ‘purple pipe’ supply delivering treated wastewater (Class A) for non-potable uses for residences as well as industry is one option. However, this is only realistic for greenfield developments.

Ideally, Professor Arora says wastewater would be treated to potable standard so that it can top up drinking water supplies. “This is technically possible, only marginally more expensive than treating to Class A – as demonstrated by Professor Peter Scales’ research – and eliminates the need for additional third pipe, so it is not restricted to greenfield sites.

“Through this project we are looking at options in India for new water and wastewater infrastructure not hampered by legacy infrastructure, as faced by Australia. We have calculated that by installing the Class A purple pipe option we would reduce the draw on potable water by 50 per cent. This will ease the pressure on highly scarce freshwater resources during drier years. And, because more wastewater will be treated and used, there will be less wastewater discharged into the environment, leading to reduced stream pollution.”

The purple pipe solution

Professor Arora says this research has implications for urban planning. “At the moment, if you design water supply infrastructure to support a new suburb of 100,000 people, that becomes the population cap. But by plumbing in a purple pipe for non-potable uses you would be building in growth capacity because you could be halving, at the start, the draw on potable water.”

The team plans to show how a small township – be it in India or rural Australia – can achieve water self-sufficiency by extending its rainwater supply through treating and storing that water, after its initial use. This water could then be resupplied either as Class A non-potable water or, with full treatment, a new potable water supply.

These are the scenarios the researchers of the ‘Integrated Urban Water Management Systems in Australia and India’ project are now testing. Their ultimate goal is to help the world preserve its most valuable resource; our water.

First published by the Faculty of Engineering and IT, University of Melbourne

First published on 19 October 2021.

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