Rainwater harvesting makes sense in dense urban areas and helps repair stormwater woes.
Booming populations and increasing floods are overburdening urban stormwater systems, so why not lighten the load by collecting rainwater for household use?
Demand on conventional “grey” stormwater infrastructure in cities – the gutters, channels and drains that collect excess rainwater – is increasing.
“The stormwater problem in Australia is probably the most urgent of our urban issues,” Kingspan Water and Energy technical and sustainability manager Michael Smit told The Fifth Estate.
The first challenge is densification: the rise of infill development means more concrete and pavers and fewer gaps between these impervious surfaces to absorb stormwater.
This piecemeal development in urban ring areas, which have been government policy in many cities (for many admirable reasons, not least preventing sprawl into bushland and farmland as populations grow), also puts pressure on existing stormwater infrastructure that was not designed to handle the additional load.
The second risk factor is climate change. Smit says that with every extra degree, the air holds around 7 per cent more water.
“Just by being warmer there’s a much larger chance of a big dump of water.”
He’s aware that the climate science is more complicated. However, the connection between climate change and flooding has not eluded risk-averse insurance companies.
In cyclone regions in northern Queensland, insurance premiums have risen by as much as 30 per cent.
Not only do these challenges leave property at risk from flood damage, but Smit says poor stormwater management also damages natural river ecosystems.
In the bush, about 40-50 per cent of rainwater is absorbed into the soil as groundwater, another 40 per cent evaporates and a mere 10 per cent runs off across the ground’s surface and into rivers and streams.
The calm trickle of groundwater into waterways is what native flora and fauna are accustomed to – not the gush of closer to 100 per cent of rainwater rushing down impervious surfaces, “washing away the plants and the platypuses”.
Research by University of Melbourne associate professor Chris Walsh and others have uncovered the damage poor stormwater management causes waterways.
Walsh found that if just 5 per cent of the impervious surfaces in a catchment area are connected – that is, there’s no patches of grass or garden beds to absorb stormwater – then the damage to natural waterways is likely to be irreparable.
Better stormwater management starts by reducing the load
More green space is undoubtedly one of the most effective solutions to curb stormwater issues, with bonus benefits such as increased biodiversity, amenity and urban cooling.
But Smit says catching rainwater using a water tank for use in homes and buildings is a complementary solution to ease the worst effects of stormwater runoff.
Rainwater harvesting can significantly lessen the burden on stormwater infrastructure simply because so much less water ends up in drains and sewer.
“It takes volume out of the system.”
Instead, rain is funnelled through roof gutters and stored in tanks to be used for watering gardens, flushing toilets, washing clothes and even drinking if it’s treated.
It’s a strategy that is more commonly directed at reducing demand on water supplies, which are also under threat from more severe, prolonged droughts caused by climate change.
The beauty of rainwater tanks an rainwater harvesting, Smit says, is that they are ideal for new infill development – even on a tight block there’s always room for a tank – especially when compared with other stormwater interventions such as retroactively putting in ponds or wetlands.
“People may think rainwater harvesting is less suitable for household retrofits but this is possible with Kingspan Water Tanks as we offer the made-to-measure option to make this work.”
There’s room for flexibility, he explains, such as choosing to connect rain gardens and permeable pavements as well.
Water tanks common in NSW but elsewhere it’s anyone’s guess
Rainwater harvesting is common in NSW thanks to the BASIX planning controls that specify minimum requirements on water efficiency and other sustainability criteria.
Outside of NSW it’s a different story, with rebates available in some states and territories but regulatory intervention to encourage rainwater harvesting is patchy.