Some experts believe the key to eliminating raw sewage overflows into Auckland Harbour lies on the roof of one of the city's recent office blocks.
A garden of low desert-like succulents and iceplants covers much of the roof of the Green Star-certified NZ Insurance building, built in Fanshawe St in 2009 and now housing the national office of the IAG insurance group.
IAG property manager Tim Griffith says the garden sits on a 50 to 75mm substrate of pumice and other inorganic and organic material. Rainwater soaks through it into a 38,000-litre tank which is used to flush the building's toilets.
The system reduces rainwater runoff to the city's drains by 75 per cent - and the benefits are not just environmental.
"There is also a financial benefit because you are not paying water charges," Griffith says.