Costs dilute water treatment

As Martinborough continues to be impacted by a boil water notice, an expert has explained why small towns are more susceptible to bouts of contamination.

Water New Zealand principal water quality adviser Jim Graham said treatment plants in smaller communities were often not up to the standard of sophisticated overseas infrastructure that made water safe without chlorination.

Graham was familiar with the Martinborough water supply and said it used a ‘‘pretty standard treatment method’’ for a town of its size.

The South Wairarapa District Council employs a ultra-violet treatment and filtration system for the extracted groundwater from its Martinborough bore source.

‘‘The reason that they don’t add chlorine is because the water has some iron and manganese in it, which is very common.

‘‘If you add chlorine, the iron and the manganese gets oxidised and it precipitates and forms a gooey sludge that comes through the taps,’’ Graham said.

These minerals can be removed to allow chlorination but it cost more.

‘‘It’s not particularly difficult but it’s another treatment stage.’’

The South Wairarapa District Council planned to spend $700,000 in two years’ time on a system to remove those minerals.

Graham said the big question was whether the E coli detected in the Martinborough water supply had come from the groundwater, and the bacteria hadn’t been killed by the UV process, or whether the contamination happened afterwards in the distribution system.

Council spokeswoman Amy Wharram said they believed contamination was coming from within the reticulation network, but they had not yet isolated the source.

Routine testing last week revealed the presence of E coli at Martinborough School and more recent tests have come up positive at a site near Martinborough’s reservoir.

Graham said it was not the E coli that was dangerous but it could be an indicator of harmful organisms such as campylobacter.

Visiting Canadian expert Dr Steve Hrudey, speaking at the Water New Zealand Drinking Water Conference in Hamilton in 2017, said there seemed to be an aversion to chlorinating water in New Zealand.

Hrudey said that without proper treatment, there was nothing stopping another outbreak similar to that in Havelock North in 2016, which made 5000 people sick.

Graham said it was possible to have a safe water supply without chlorine.

‘‘It certainly is possible because they do it in the Netherlands, Denmark and Germany.

But in those places, they have strict rules and [are] well-run, well-resourced and [have] very modern water supplies. ‘‘We don’t have that. ‘‘Water supplies in New Zealand, particularly in small areas, tend to suffer from deferred investment.

‘‘They can be a down,’’ Graham said.

He said it was best to chlorinate small water supplies because it gave them an extra level of safety.

‘‘Water supplies in New Zealand, particularly in small areas, tend to suffer from deferred investment. They can be a little run down.’’ Water NZ principal water quality adviser Jim Graham

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