Chris Walsh has an unusual obsession — making his house and garden as stormwater smart as possible.

When he renovated five years ago, he prioritised including a rainwater tank and rain garden to absorb and purify stormwater and test how much of a difference it would make.

"We've reduced our water consumption by a third in this house," Associate Professor Walsh, who lives in the Melbourne suburb of Richmond, said.

"In 95 per cent of rain events we have no runoff from the property at all."

How big a problem is stormwater?

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Stormwater is water that drains off a site from rain that falls on the roof and land, taking with it soil, organic matter, litter, fertilisers from soil and other pollutants.

It is estimated 3,000 gigalitres of stormwater runoff is produced in Australia's urban areas each year — the equivalent of six Sydney Harbours or 1.2 million Olympic-sized swimming pools.

"In a natural environment, typically around 80 per cent of the rain that falls actually just gets evaporated up into the atmosphere," University of Melbourne Professor Tim Fletcher said.

"But in an urban environment about 90 per cent of that rainfall becomes runoff going straight into our streams, so there's this massive excess, something like five times the natural amount of runoff is going into our streams and cities."

It's not uncommon to see streets filled with stormwater after it rains. ( ABC News: Marcus Alborn )

Professor Fletcher said that in most Australian cities, the amount of stormwater runoff each year was equivalent to the total water demand of that city.

"It's like we're giving away gold," Professor Fletcher said.

So, what's a rain garden?

While a rainwater tank is a common sight in Australian backyards, a rain garden is a slightly less familiar concept.

A rain garden is specially designed to collect stormwater runoff from nearby sources, such as roofs and drains, and filter it to remove nutrients and pollutants.

A rain garden works by running water through several layers of different sediment. ( Supplied: Melbourne Water )

What that means, is that instead of polluted water washing from a property into a drain or onto the streets, the water is cleaned and can be collected.

Water can then be used to irrigate the garden or can be released without the pollutants into the drainage system.

Chris Walsh says there is no runoff from his property in 95 per cent of rain events. ( ABC News: Annah Fromberg )

Associate Professor Walsh, who is also a water researcher at the University of Melbourne, says his backyard stormwater system saves about $150 a year on bills.

He also estimates his homegrown vegetables, fruit and herbs, which he does not have to water, as being worth hundreds more per year.

Associate Professor Walsh said his "design is pretty simple" and involves runoff from his roof going into the rainwater tank, with any overflow directed to the rain gardens in front and back of his house.

"There are a whole lot of different sorts of rain gardens and this is just one sort," he said.

"These particular rain gardens are completely sealed so they're really like planter pots and they've always got water in them so they're completely self watering.

"If you had a bit more space and you didn't have buildings right up against your boundary you could have them infiltrate into the ground and that's another sort of rain garden."

What impacts do they have?

Associate Professor Walsh believes that if more Australians made a few changes to their properties, it would boost the country's water supplies and reduce the amount of toxic pollution entering our creeks, rivers and beaches.

Stormwater washes pollutants like fertiliser into our drainage system. ( ABC News: Tim Callanan )

"If all houses across a city like Melbourne had a system in place where [stormwater] was not overflowing into the street very often, we'd certainly decrease our flooding risks," he said.

"We'd also start working towards having much healthier rivers and we'd be using a lot less water from our reservoirs and increasing our water supply security."

Brisbane civil and environmental engineer and Stormwater Australia president Alan Hoban agreed, and said if stormwater was harvested on a broad scale across Australia's urban areas it would make a big difference to dam levels.

"You can significantly reduce the amount of water restrictions by harvesting rainwater and stormwater," Mr Hoban said.

"It's really important that we all think about capturing and re-using stormwater because what happens at every individual house matters, the cumulative impact of everyone's house make a really big impact to the health of our creeks, rivers and our oceans."

Rain gardens can look unassuming. ( ABC: Ann Jones )

Rain gardens are also money-makers, according to evidence given to a federal parliamentary inquiry into stormwater resources in 2015.

Research done for the Cooperative Research Centre (CRC) for Water Sensitive Cities examined property sales in Sydney between January 2008 and September 2014 and found houses sold for at least $50,000 more when a rain garden was less than 50 metres away.

"On the pure amenity value, we see a huge return," Professor Ana Deletic, a University of New South Wales stormwater researcher and one of the experts working within the CRC for Water Sensitive Cities, said.

Another study by the CRC found houses with rainwater tanks also fetch higher prices, with an analysis in Perth suggesting there was a premium of up to $18,000 built into the sale prices of houses with tanks installed.

What if I live in an apartment?

All this works well if you own a property you can modify, but with many homeowners in capital cities living in apartments or townhouses, it might not seem feasible to install a rain garden.

That is why developers of some apartment complexes are turning to green roofs — vegetated landscapes on top of buildings, which are often installed as design features, as well as for their stormwater capturing ability.

In addition to reducing stormwater runoff, experts say green roofs have psychological benefits. ( Supplied: Urban Water/City of Melbourne )

They act "like a sponge, just like the natural landscape," according to Melbourne University researcher Claire Farrell.

"It's really mimicking the natural landscape in a cleverly engineered way."

Scientists at the University of Melbourne have determined stormwater runoff in our capital cities could be reduced by up to 85 per cent if our capital cities were transformed into green sponges through the addition of rain gardens, green roofs and green walls.

Could cities look like this in the future? ( Supplied: City of Melbourne Urban Forest Fund/Anton Malishev )

Dr Farrell said green roofs didn't need to be confined to apartment buildings, but could be installed on any structure, including car parks and railway stations.

And they have other benefits.

"Viewing green roofs for even 40 seconds can improve workplace productivity, they also cool buildings," Dr Farrell said.

In the Melbourne suburb of Lyndhurst, a new affordable housing development is using rainwater and recycled water to reduce its reliance on drinking water from reservoirs by up to 70 per cent.

Charlie Littlefair, general manager of Liveable Water Solutions at South-East Water, one of the partners in the project, said the development was ground breaking in a water efficiency sense.

"So the 42 hectares of this development, every home, all 460 will have all three of those sources of water [rainwater, recycled water and reservoir water]," he said.

Green roofs aren't limited to apartment buildings, they can be on top of anything. ( ABC News: Annah Fromberg )

Are backyard solutions enough?

While individuals are coming up with a range of water solutions, Mr Hoban said coordinated planning at a state and federal level was needed to ensure Australia's growing urban populations continued to have access to enough drinking water.

"There's a whole lot of regional planning that state governments can do in creating co-ordinated policies that work right across urban environments," he said, calling for more research funding at an "Australian-government level".

But all experts agreed individuals could make big contributions.

"If you are in the process of building your own house or renovating your house it's not a lot of extra effort to add to the bill to think carefully about the way you manage stormwater on your property", Associate Professor Walsh said.