Editorial: Ditching dual water plan makes sense

The residential development Stonefields in Mt Wellington, Auckland. Photo / Richard Robinson

Stonefields idea would be money down the drain.

Stonefields, a village-style residential development in what was the Mt Wellington quarry, has branded itself with environmental "sustainability". The basis of that brand was a dual water supply. Every house built so far has both a drinking-water supply and a "third pipe", bringing surface water from a central reservoir to toilets and outside taps. The system may have saved water from the metropolitan supplier, Watercare Services, but saving water is not the supplier's prime concern.

Many, in fact, will suspect the monopoly supplier's refusal to operate Stonefields' scheme as intended is motivated by the simple desire to maximise its revenue. Not so, says Watercare. The scheme, it says, would have cost Stonefields residents more than they will pay for the normal water supply. And since the groundwater collected for the third pipe would not have been treated to the same standard, it would have been charging those residents more for a supply of lower quality.

Common sense is probably on the side of Watercare. Surface run-off, especially from roads, is polluted. It was going to have to be treated as it was pumped from Stonefields' collection tank to the reservoir, though not to a drinkable standard. The company says the cost of collection, treatment and pumping would have resulted in Stonefields residents paying five times the cost of Auckland's potable water. And most of the third-pipe water would be flushed into the same second pipe, where it would need sewage treatment and disposal.

Cost is not the only consideration. Enthusiasts for third-pipe water conservation ought to consider what would be lost. This is a country in which the water is safe to drink. To slake a thirst, we turn on the nearest tap without a qualm. That would change if not all piped water could be trusted. The outside taps at Stonefields were to carry a sign that the water was not safe to drink. Do we really want that?

The former Auckland City Council ought to have thought of all these practicalities before it invoked principles of sustainability and made third-pipe reticulation a feature of Stonefields' development consent. Its own water retailer, Metrowater, was going to run the system. But for the Super City's creation, and the bulk supplier's takeover of the whole system, the true costs of "sustainability" might never have been known.

Stonefields residents might not have compared their bills with those beyond the development. The water use of any two houses is hard to compare. Possibly the residents would have considered the additional cost worthwhile for the sake of knowing they were drawing less water from the municipal supply. But few complaints have been heard from the residents since we reported Watercare has pulled the plug. Their third pipe now carries the same treated water as every other pipe.

Thanks to the Waikato River, Auckland will never be short of water. There is no point conserving the water for its own sake if it must be replaced by a costly supply of inferior standard, no matter how interesting or exciting the environmental engineering involved.

More water falls on Auckland than the city can use. Only a fraction of Stonefields' stormwater was to be channelled into the third pipe. Most would have drained to the Tamaki inlet. Reducing stormwater pollution of the sea around Auckland is the real challenge. Collecting tanks and treatment may be the answer, and if the water can be put to a cost-effective use, all the better. But recycling for a needless purpose at greater cost is not sustainable.