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Our water: groundwater quality

As part of its National Environmental Reporting Programme, the Ministry for the Environment regularly reports on water quality in groundwater aquifers. This information sheet presents the key findings from data collected from over 900 groundwater sites throughout New Zealand between 1995 and 2008.

As part of its National Environmental Reporting Programme, the Ministry for the Environment regularly reports on water quality in groundwater aquifers.

Data collected from over 900 groundwater sites throughout New Zealand between 1995 and 2008 was analysed for compliance with relevant guidelines and to identify national and regional trends.

Key findings

Nitrate and Escherichia coli

  • Five per cent of sites had median concentrations of nitrate that exceeded the health-related drinking water guideline of 11.3 mg/L (although many sites will not be used for drinking water supply).
  • Faecal contamination was indicated by the presence of E. coli at 23 per cent of monitoring sites. This may be more indicative of poor well-head protection than overall groundwater quality.
  • Nitrate and E. coli contamination was especially common in shallow groundwater.  Shallow groundwater is most vulnerable to the effects of human activities on the land.

Median Nitrate

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Map showing median nitrate for the period 1995 to 2008 for 914 groundwater sites in New Zealand. The majority (80%) of sites have median nitrate levels less than 5.65 mg/L. Forty four (5%) sites have median nitrate levels that exceed the drinking water guideline of 11.3 mg/L.

 

Trends in groundwater quality

  • Groundwater quality is stable or changing slowly (probably due to natural processes) at around three quarters of sites.
  • About one third of sites showed significant changes in nitrate levels between 1995 and 2008. Of these, more have increasing (deteriorating) trends than decreasing (improving) trends.

Regional Trends in Nitrate, 1995-2008

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Region % of sites with significant decreasing trend % of sites with no significant trend % of sites with significant increasing trend
New Zealand total 11.85 68.17 19.98
Auckland 28.6 57.1 14.3
Bay of Plenty 7.5 86.8 5.7
Canterbury 5.9 64.3 29.8
Hawke's Bay 8.9 73.3 17.8
Manawatu 19.0 71.4 9.5
Marlborough 8.7 69.6 21.7
Northland 8.1 83.8 8.1
Otago 11.2 76.5 12.2
Southland 12.2 68.3 19.5
Taranaki 12.9 80.0 7.1
Tasman 18.8 56.3 25.0
Waikato 20.0 47.3 32.7
Wellington 19.7 74.6 5.6
West Coast 0.0 50.0 50.0

This information supports the Government’s New Start for Fresh Water work programme and other freshwater policy initiatives.

FOR MORE INFORMATION go to National Groundwater Quality Indicators Update: State and Trends 1995-2008

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November 2009
Ref. INFO 457

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