Families on bottled water after ‘shock’ nitrate results
When Martin Hewitt moved to the North Canterbury settlement of Ohoka during the mid 1990s, tests of the drinking water from his well showed nitrate levels of 2.4mg/L.
Two weeks ago, a sample from Hewitt’s bore came back at 20.4mg/L.
“It was quite a shock, and we’ve been drinking the water for all that time.”
The reading, almost double the maximum allowable value for nitrate nitrogen (11.3mg/L), was the highest reading from about 450 public and private samples recently tested by Greenpeace.
Nitrate-nitrogen (commonly referred to as nitrates) in waterways comes primarily from excess use of nitrogen fertilisers and the nitrogen-rich urine of cows, which can seep through the soil and into waterways and underground aquifers.
High nitrate levels in drinking water have become a known problem for some private bores, which district and regional authorities say they have no obligation to monitor.
Thousands of Cantabrians drink water from private water supplies, including nearly 7000 in the Waimakariri district alone.
Hewitt realises he should have tested his water earlier, especially as surrounding land use changed from predominantly sheep farming to dairying.
He’s worried about the potential longterm health impacts, as well the effect on his property value. He and his wife have used bottled water for drinking and teeth brushing since finding out.
He has applied to the Waimakariri District Council to connect to the Ohoka water supply, but understood the cost could be $5000 to $10,000.
Luis Arevelo and his wife have been drinking and cooking with bottled water since moving to Oxford, and get through 30 to 40 litres a week.
He said high nitrate levels in the area were common knowledge, but it was still
a shock when their Waimakariri District Council-supplied water came back at 5.35mg/L.
He’s joined a new community-led action group pushing for more transparency and better health outcomes.
A Waimakariri District Council statement said the council tested public water supplies for nitrates monthly and all were less than half the maximum allowable value.
ECan declined to comment, but on its website says it has introduced “some of the strictest farming rules in the country,” and allowed “very few” dairy conversions in recent years.
However, it warns groundwater quality may not improve for at least another 15 to 20 years, and that in some cases “we can expect the situation to get worse before it gets better”.
Nitrate infiltration into ground water has been a growing issue across the Canterbury plains for decades.
Campaigners argue the maximum limit of 11.3mg/L which is based on 1958 World Health Organisation guidelines to prevent babies dying from methaemoglobinaemia (blue baby syndrome), is too high for human and waterway health.
A 2002 ECan technical report by Carl Hanson – who is now the council’s groundwater science manager – noted high nitrate concentrations had been observed in the south and west of Christchurch since the 1970s, and that research dating back to the 1980s predicted new irrigation schemes and more intensive land use could lead to higher nitrate concentrations in groundwater, “threatening its suitability” as drinking water.
The report warned of a “number of bores already testing over half the maximum allowable value” across swathes of the plains, particularly the Ashburton-Pendarves area, the south and west of Christchurch, and the area between the Waimakariri and Ashley rivers.