A baby could die if nitrate levels in the water in some areas of Canterbury are not more tightly controlled, a health official says.

Canterbury District Health Board medical officer of health Alistair Humphrey said wells near Ashburton had high nitrate levels, which could cause methaemaglobinaemia in infants.

The condition affects blood by converting a substance to a chemical that cannot deliver oxygen to tissues. It occurs after consumption of nitrates either during pregnancy or by bottle-feeding. Babies under 6 months old are most at risk. "That problem could end up as a tragedy," Humphrey said. "Sooner or later a baby is going to be fed with nitrate and die."

Environment Canterbury's annual groundwater quality survey in 2010 found nitrate levels had been increasing in about one- third of the wells during the past 10 years, particularly in the Selwyn, Ashburton and Orari-Opihi-Pareora zones.

Of the 322 Canterbury wells tested, 34 had levels of nitrate that exceeded the maximum acceptable value for drinking-water standards.

Humphrey presented his concerns, along with ECan's data, to the Ashburton water management zone committee in June but said he was "upset" by the lack of concern.

"If they mix it [formula] up with nitrate it will be like putting a baby in a car with a hose pipe from the exhaust going into the car."

He said it was likely if the water committee did not act to reverse the trend of nitrates in the groundwater that it would end in tragedy.

"It is rare, admittedly, but it is a real risk and it may be more common than the data suggests." Humphrey said the health board was working with maternity carers to ensure pregnant women and mothers knew about the risks of consuming water with high nitrate levels, but could not guarantee all new mothers were aware.

Water committee chairman Matthew Hall said members were not going to sit on "our bottoms", as it was a "high-priority" issue.

He said the committee needed more information before it made recommendations on how to handle the problem.

However, it was a small number of wells where there was potentially an issue and everyone on farms either had their water tested or knew not to drink it, he said.

- © Fairfax NZ News

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