Thousands of new homeowners are being forced to install water tanks to protect the environment - a move that could end up saving them thousands of dollars.
Local authorities are investigating ways to stop water being flushed down the drain needlessly, not to save ratepayers money, but to stop fragile streams being flooded.
However, the $3000 price tag for a water tank can be recouped in water bill savings in just three years - a great return, when water in Auckland costs four times as much as it does in Christchurch (see table). In the past three years, more than 2000 homes on Auckland's North Shore had had rain tanks installed, said Jan Heijs, infrastructure planner for North Shore City Council.
Proposed district plan changes mean thousands more will be needed for subdivisions across the booming city, although an Environment Court appeal has been lodged by a developer for a project in Long Bay.
While most Australian cities now required new homes to have a tank to save water, Heijs said the North Shore council's regulations were simply to save the fragile ecosystem.
"I think we're at the forefront, although other councils will look at it," Heijs said.
"If you capture water from the roof you can hold it, then use it. Then it's not going into the stormwater and helps protect our streams."
The "pipe and forget" approach was no longer working, he said. So instead of building kilometres of stormwater pipes, the onus was being put on builders of new homes to help reduce their impact on the environment.
It cost $2980 (plus GST) to have a 4500-litre tank delivered to your home, Christian Maarshuis, of Jacobs Water Tanks, said.
The average annual water bill for an Auckland family of four is between $1000 and $1200, meaning the cost could be recouped in water bill savings within a few years.
However, the water was classed for "non-potable use" - in the laundry, toilet and outdoor - and should not be used for drinking.
Despite the serious health risks, more than 400,000 New Zealanders rely on rainwater to drink. Earlier this year, the Auckland Regional Public Health Service warned homeowners to keep tanks clean to prevent disease.
Dr Denise Barnfather said ideally tanks should be inspected and cleaned each year to stop animal or human faeces, sewage, leaves and other debris contaminating the water - which causes diarrhoea and vomiting.
The health alert was backed up by a recent five-year Massey University study which found many roof tanks contained seriously contaminated water.
In a sample of 560 tanks, at least half exceeded the acceptable standards for contamination, and more than 30 per cent had evidence of heavy faecal matter, according to the study by Stan Abbott, senior lecturer of microbiology and communicable diseases.
This week, water prices in Auckland and across the country will be investigated by a parliamentary select committee. Auckland City Council, meanwhile, has backed down from plans to raise water bills over 10 years, but will still raise them by more than 9 per cent next year.
WaterCare sells water to five Auckland councils at 45c a kilolitre. The councils sell it to ratepayers for anywhere between $1.14 (Manukau) and $1.48 a kilolitre (Waitakere). Auckland City's Metrowater charges $1.28.
Auckland City had planned to raise Metrowater bills by between 9 and 10 per cent a year for 10 years to raise $280 million, an exercise labelled "smoke and mirrors" by Green Party councillor Neil Abel, amounting to a hidden rates rise.