Canterbury Regional Council figures show that for the ten years
to the end of 2016, nitrate levels increased in 23 percent of
So far, high nitrate levels in Canterbury were confined to
private wells and none of those serving communities had been found
to have dangerously high readings.
However, a quarter of council-monitored wells are coming close
to exceeding safe limits.
Nitrates are harmless to adults but risk blue baby syndrome,
which can be fatal to newborns, Canterbury medical officer of
health Alistair Humphrey said.
"We don't know how many babies have been affected, not all will
die," Dr Humphrey said.
"We certainly have anecdotal accounts from mothers in the
Canterbury region whose babies have been very unwell and then when
they have removed the high nitrate water, their babies have
He said there had only been one confirmed death from blue baby
syndrome, but the actual number of deaths could be higher as some
may have been mistakenly attributed to sudden infant death
Increased irrigation and the dairy farms it supported were to
blame for the increased risk posed to infants, he said.
Dr Humphrey has
previously supported Greenpeace campaigns to reduce the
number of cows allowed on farms.
Council groundwater science manager Carl Hanson said irrigators
with higher nitrate levels were concentrated in farming areas
running south from Christchurch to Ashburton.
"Farming has become more intense and that means you need to have
more nutrient, more nitrate available in the soil for plants to
grow and that leads to more nitrate leaching."
While only 7 percent of monitored wells exceeded the safe
drinking water standards for nitrates, 25 percent were coming
close, he said.
"They're not above the limit so they are still potable, but it's
just sort of a flag that the concentration is maybe getting up
there and so they need to do extra monitoring to make sure that the
concentration stays below the limit, and that's the responsibility
of the water supplier."
Council acting chair Steve Lowndes said he, like many, struggled
with the twin targets the council had to meet under planning rules
to increase the amount of irrigated land on the Canterbury Plains
while at the same time improving water quality.
Irrigation would not be used to grow grass for cows in the
future, he said.
"We will be going in to much more finely tuned agricultural
endeavours. So, irrigation isn't the bugbear. It is actually
historically what it has been used for and that is what we're
trying to change."