Bore & Well Water

Information for people whose household water supply comes from a bore or well.

If your water comes from a bore or a well (general groundwater), there are things you need to know.

Water used for drinking, teeth-cleaning, hand-washing, bathing, showering, food preparation and cooking needs to be free from harmful germs and chemicals. So does drinking-water for stock and pets.

Clear water does not always mean the water is safe. The only way to know if your groundwater is safe is through regular laboratory testing. Your local council or public health unit can advise about testing.

Nitrates and nitrites - Frequently Asked Questions

How does nitrogen get into my water supply?

Nitrates (NO−3) and nitrites (NO−2) are formed when nitrogen combines with oxygen. They are easily dissolved in water and can be transported through soil and into groundwater.

Whilst natural vegetation can increase groundwater nitrate levels, most sources of increased nitrates in surface level and groundwater are due to human activities. For example;

  • fertiliser application
  • animal waste from high density dairy grazing
  • disposal of dairy factory wastewater
  • unreticulated sewage disposal
  • industrial and food processing waste.

On-site waste disposal systems (e.g. septic tanks) can also increase local nitrate concentrations (NZDW).

Are nitrate levels in drinking-water monitored?

Rural drinking water bores and wells are at risk of having elevated nitrate levels. Testing can be done to ensure levels are below the Maximum Acceptable Value (MAV). Please contact your local council if you would like your bore or well water tested for nitrates.

What does the Maximum Acceptable Values (MAV) mean?

If a test result is below the MAV, the risk of getting disease from drinking that water is thought to be very low.

For nitrates, the Drinking Water Standards for New Zealand have set the MAV at 50mg/L for nitrate which is equivalent to 11.3mg/L of nitrate-nitrogen.

It is important to ensure that levels are interpreted using the correct units.

Are nitrate levels constant?

Whilst surface water concentrations of nitrates can change rapidly, groundwater changes generally occur more slowly. Increased rainfall or rising water table levels can cause increased leaching of nitrate from soil. Levels are usually highest in winter and spring.

What are the risks of drinking water that is high in nitrates?

Drinking water that has high levels of nitrates can pose health risks to pregnant women (and their unborn babies), formula-fed babies in their first six months of life, and adults with rare metabolic disorders. Nitrates interfere with the way our bodies transport oxygen in our blood and can impact the function of the thyroid gland.

What is ‘blue baby syndrome’?

Unborn babies and infants under six months of age are at risk of developing ‘blue baby syndrome’ when they are exposed to nitrates. Their bodies have a different way of using oxygen compared to older children and adults. Nitrates interfere with the way their bodies use oxygen. The skin around their mouth and on their hands and feet may appear blue. Severe cases of ‘blue baby syndrome’ can cause breathing problems and can be life threatening.

Although extremely high levels of nitrate intake can cause problems in adults and children, bottle-fed infants under six months of age who receive formula prepared with water that is high in nitrates/nitrites are most at risk of this condition. This risk may be increased when the baby also has a tummy bug.

How can I decrease the risk?

If tests show that the level of nitrate is close to or above the MAV, pregnant women should use an alternative drinking-water source (e.g. bottled water or water from a reticulated water supply). Alternative water sources should be used to prepare formula for bottle-fed infants under six months of age. The most effective measure to control nitrate concentrations is to reduce the chance of contamination.




Last updated: Wednesday, February 27, 2019

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