Case study - greywater recycling at Waterstone subdivision in Kapiti

Water conservation was a priority - and a council requirement - for the developers of Waterstone, a new Paraparumu subdivision.

With more and more subdivisions appearing on the New Zealand landscape, councils everywhere have to take a serious look at household water usage. One such example is Waterstone, a new Kapiti Coast subdivision, where greywater recycling has been used as a means of water conservation.

Building company Home Creators decided to use Watersmart's greywater recycling gullies

"Since the early 1990s, the Council requirement for land not previously residential has been a trickle-fed system, allowing 1000 litres of water a day per household, restricted to 40 litres per hour," says Kapiti Coast District Council's water coordinator, Ben Thompson. "This is so the infrastructure can handle the additional residential demand."

One thousand litres a day is for household use only, says Ben, so an alternative water source for outside water use is clearly a must. Along with a storage tank for the potable water supply, the council recommended 10,000 litres of rainwater storage for each lot - with options open to discussion.

One possibility was to use bore water, but the local shallow groundwater is heavy in iron and manganese and could cause staining.

A second, more unusual, option was to incorporate a greywater recycling system. Local company WaterSmart came on board at this stage to demonstrate the benefits of their innovative new gully system, which gives homeowners the choice of diverting water from their bath, basin, shower and washing machine into an underground irrigation system, or into the regular sewer.

Home Creators, one of the building companies involved in the subdivision, was won over. "The Council wanted a 10,000 litre rainwater on each property. That's a big tank to bury - and no one wants them above ground," says Paul March of Home Creators. "With a 650 sq m section, and a 220 sq m house, there was also not much space left to bury such a big tank. Plus, a tank that size is quite expensive, and adds about $10,000 to the price of the house."

By using the Watersmart system, the size of the rainwater tank could be reduced to 6340 litres - cheaper, smaller and more manageable for burying beneath the ground.

Watersmart director Steve Roberts designed the greywater recycling systems for the properties, and sourced the rainwater tanks. Meanwhile, Master Plumber Bruce Bryant, of Bryant Plumbing and Maintenance Ltd in Waikanae, was contracted to install the systems.

"We were working in conjunction with the Council to find ways down here on the coast of saving water. We haven't had any problems this year, but in previous years it's been bad for water shortages," says Bruce.

Initially, a Watersmart gully was installed in some council flats as a trial, and this was followed by two installations at the subdivision. "It's pretty easy to install in a new house," says Bruce, "and by using the gullies, we could put in a smaller holding tank feeding the hose taps and irrigation. If you're fitting it in an existing drainage system, you have to dig the system up and make sure you have the right depth and falls."

To date, Bruce has installed five Watersmart systems at the subdivision, one of which is in the show home. Another has now been put to the test, with the first homeowner moving in a week ago.

Greywater recycling was a pretty new concept to Bruce, but he says he can see a time when it will become more common. "Water supply isn't getting greater, and people are going to have to look at ways of saving water."

Ben Thompson at the Council agrees. "If everyone had a greywater system in place you could extend the life of both the water supply and the sewage systems."