Suburbs dropped to lift water quality rating

The north-western suburbs have been hived off from the rest of Christchurch by the city council in a bid to improve its water-quality rating.

The move to separate suburbs such as Fendalton and Burnside means Christchurch has escaped a D grade for its drinking water.

New Ministry of Health figures measuring the risk of water contamination give a Da for the north-west of Christchurch and a Ba for the remainder of the city.

The whole of Christchurch had previously been a Ba, the highest grade it can receive without treatment.

The lowest grade is E and the highest is Aa.

Community and Public Health drinking-water assessor Judy Williamson said the council had changed its water grading boundaries when they were made aware of the Da rating.

"If you have got several reticulation zones, then the overall grading is a reflection of the lowest grade. Christchurch would have got a Da, so they (the council) re-registered the north-west as a completely separate community," she said.

The capital "D" was the grade for the water source and treatment plant and the small "a" referred to the water reticulation infrastructure and its management, Williamson said.

"If the population is greater than 10,000, the source and treatment should be `B' and distribution should be `a', so Christchurch is not getting there," she said.

The Waimakariri River was the source of much of the water in the north-west (population 83,000). The water was often less than a year old when it reached the taps.

The rest of the city used groundwater from the Canterbury Plains, which could be 70 to 80 years old, she said.

The problem with young water was the higher risk of contamination.

Of the 150 wells in Christchurch, 40 were in the west, and 10 of those used water that was less than a year old.

"The potential is there for it to be contaminated, so it's only a D," Williamson said.

To receive a higher grade, the council would have to dig deeper wells or treat the water.

"We are taking samples often and complying with other standards, so it's well managed," she said.

The council had been proactive in getting its public health risk management plan approved, Williamson said.

"They (the council) are definitely thinking about it. They don't like having a D," she said.

Council network planning team leader Simon Collins said the council decided to re-register the north-west area when the security of its wells came into question.

"Canterbury Public Health agreed that it was unnecessarily harsh to have the whole city graded as Da when three-quarters was perfectly OK. The fact is the water's the same it's always been for the last 100 years," he said.

"We think the new standards treat Christchurch particularly harshly because they are really written for typical supplies around the rest of the country where they put chlorine in it."

The Christchurch public would be "horrified" if the council started talking about chlorinating the water and it was not something that was being considered, Collins said.

Water in the north-west was tested every day for contamination, while for the rest of the city it was just once a month.

Since January 2005, more than 3000 samples had been taken, of which five showed the presence of E. coli. Follow-up tests were clear, he said.

If there was major contamination it would be quickly detected and water could be pumped in from the rest of the city, he said.

Last year, Environment Canterbury (ECan) proposed a variation to its natural resources regional plan to restrict land use and protect the Waimakariri water supply.

Burnside resident Annette Waites said the Da rating was a concern. "We have just been told by TV don't drink bottled water because it's perfectly good out of the tap, and then you hear this," she said.

 

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