As our urban population swells, so too does our demand for water.
According to the United Nations, 2.7 billion people across the globe will face severe water shortages by 2025 if current rates of consumption continue. That’s more than a third of the world’s population. A further 2.5 billion will live in places where it is difficult to find enough fresh water to meet their daily needs.
As the driest inhabited continent, Australia will not be immune to this problem. According to the Australian Bureau of Meteorology, eastern Australia is experiencing yet another El Niño effect, with hot days and below average rainfall reminding us that the impacts of climate change are real. So how do we guarantee the water security of our cities?
While there will never be one ‘silver bullet’ answer to the question of water management, if we are to sustain our supply for future generations, Australia must do three key things: scale up, diversify and save at the source.
According to the United Nations, the built environment consumes around 40 per cent of the world’s water resources. This, despite the fact that the commercial building sector is more water-efficient than ever before. Green Star buildings use 51 per cent less water on average than their non-sustainable counterparts, and rainwater capture, storage and recycling have become standard inclusions in many new structures.
When it comes to ensuring projects are Green Star calibre and water-saving, success at the individual building level must be scaled up.
The blackwater treatment plant at Sydney’s Darling Quarter precinct provides a great example of the scaled-up thinking we need.
The plant mines sewerage from Sydney Water’s main lines, using a sophisticated dual fixed-film biological process to transform this waste into water. The resulting non-potable resource supplies toilets and irrigation systems, as well as cooling towers in the precinct’s main building, Commonwealth Bank Place.
When combined with other water-saving measures, blackwater is reducing the amount of drinkable water used at Darling Quarter by up to 92 per cent annually. That’s 52 million litres, or 20 Olympic-sized swimming pools each year.
Given the success on Darling Quarter, why aren’t we aiming to reduce the potable water use of entire cities by 92 per cent?
Other countries are already adopting this scaled-up mentality. In Singapore, for example, 30 per cent of the nation’s water needs are currently met by ‘NEWater’ – recycled water that is purified using advanced membrane technologies and ultra-violet disinfection.
NEWater is primarily used to supply non-potable end uses, however in times of drought, Singapore uses it to supplement its drinking water. NEWater is mixed into city reservoirs, where it undergoes yet another round of treatment before reaching consumers’ homes.
Diversify or die
When water is drawn from a single supply, the risk of depleting or permanently damaging that source increases exponentially.
When Europeans first settled in Australia in the 1780s, the ‘Tank Stream’ that flowed through the new settlement in Sydney was quickly commandeered as the source of all fresh water for the colony. The Tank Stream was overused and poorly managed, and in less than 40 years, Sydney’s first water source had become so polluted it was unsafe to drink. Now it is nothing more than a footnote in history books.
Australia can learn from the lessons of other nations whose battle with scarcity has led them to diversify their water sources and adopt innovative capture techniques.
In South America, fog harvesting is helping water-poor areas to harness a previously untapped source from the air. Researchers from the Massachusetts Institute of Technology (MIT) developed a mesh net in 2013 which can capture up to 12 litres of water per square metre in foggy conditions.
Other urban centres are looking inward for water harvesting opportunities, with ‘blue roofs’ transforming city skylines into a mechanism for water retention. Designed to absorb rainwater and significantly slow (if not completely arrest) runoff, water from blue roofs can be used to supply irrigation, cooling systems and a host of other non-potable uses.
As an added benefit, by slowing the rate of discharge to urban stormwater systems, blue roofs are making cities more resilient by reducing the amount of contaminants reaching rivers and groundwater aquifers, as well as incidences of flash flooding.
Investment in desalination is another area we must consider. Not without their controversy, large desalination plants are already found in many of our capital cities. In times of heavy rain they may appear a waste of money, but in times of drought, supplementing water sources through this technology makes sense.
Think globally, act locally
Thinking big when it comes to saving water is certainly important, but a localised approach is also key. After all, the less water we use and the more we can retain close to where it is used, the better off we’ll be.
Recent drought conditions in California have led the City of San Francisco to pass legislation making it compulsory for new buildings of around 20,000 square metres or more to install onsite water reuse systems. For new buildings larger than 3,700 square metres, builders must consult with the City’s public utilities commission about the installation of greywater and blackwater systems.
Mandatory recycling is a bold move in San Francisco, but Australian cities are also doing great work to protect our water supplies and maintain the health of local catchments.
For example, by installing permeable bluestone pavers in footpaths rather than the traditional sealed alternative, the City of Melbourne is restricting the volume of stormwater entering the Yarra River while reducing the amount of potable water used to irrigate the city’s trees.
Melburnians are also embracing the ‘city as catchment’ philosophy by adopting large-scale stormwater harvesting, building reservoirs throughout the CBD and integrating stormwater into urban supply. The Darling Street system in East Melbourne, for instance, diverts stormwater from existing drains in adjoining streets, capturing an estimated 21 million litres of stormwater each year – the equivalent of saving more than 18 Olympic swimming pools worth of water annually.
‘Raingardens’ or bioswales are another initiative that Melbourne is using to keep its water local and catchment clean. Landscaped gardens in North Melbourne are soaking up excess water from the street before it is lost to stormwater drains. The plants then act as a natural filter, eliminating harmful toxins like phosphorus and nitrogen that would otherwise end up in local rivers.
Saying no to water woe
Without water, there is no life. Without water, there can be no cities. When we envisage our nation in 20, 50, or 100 years’ time, we must imagine an urban water network where no drop is wasted. Achieving this goal may be difficult, but if we scale up our successes, diversify our sources, and keep our water clean and close to home, Australia will be well on its way to future that’s water secure.