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Private water supplies

Private water supplies

Updated 16 December 2019 12:50pm
Is your private water supply safe?

Knowing where the water you drink, wash your food, and bathe in comes from is important.

It will help you to protect you and your family and friends from the chemicals or bacteria that may make the water unsafe.

Contaminated water can cause serious illness (vomiting and diarrhoea) and even be life-threatening for infants, older people, or people with weak immune systems.

If water comes into your taps from a private water supply such as a groundwater well, a roof rainwater collection tank or a stream, river, lake or spring, then you’re responsible for understanding the quality of this water and how to keep it safe for use.

If you notice changes in the colour, odour, or taste of your water or that it is suddenly cloudy, then your water may be contaminated and you need to get it tested by a qualified laboratory water treatment expert.

On this page you’ll find information to help you:

We have created a brochure covering useful information on this topic, which you can download here.

 Understanding where your water supply comes from

1. Groundwater wells

Rainfall or river water that naturally seeps into the earth becomes groundwater. Groundwater quality is influenced by the geology it flows through which means that natural impurities can end up in your well water supply. 

Chemicals and bacteria from overlying land can also flow with the water as it moves from the earth’s surface into groundwater. While the time the water takes to filter through soil and gravel can help reduce these contaminants, there’s still a risk of bacteria and chemicals from farming, gardening, landfills, storm water drains, septic or fuel storage tanks entering your well water.

Sometimes even water from irrigation or soak pits can become groundwater too. 


2. Stream, river, or spring

Streams, river, lakes and springs are surface water sources that can also be affected by factors like those that effect groundwater.

Contamination and bacteria can also flow into streams, rivers, and lake water through a storm water pipe or run off from land. Unlike groundwater, surface water isn’t filtered by the soil.

Sources of groundwater contamination

3. Roof rainwater collection tank water

Roof water collection can become unsafe when leaf litter, debris, animal droppings from birds and possums or even dead animals and insects build up in gutters or water tanks. 

Additional factors that can also contaminate roof water include:

  • Flashing or roof paint (introducing lead into the collected water)
  • Ash from household fireplace
  • Chemical spray drift (from agricultural and horticultural practices)
  • Chemical residues from road vehicle emissions.
Check your tank has a cover and doesn't have cracks or holes in it to prevent soil or other matter getting into the tank or let rainwater drain out. 

 How do I protect my drinking water supply? 

1. Groundwater wells

Make sure your well head (top of the well) is above the ground’s surface where it will not be at risk of being flooded.  You should also have a good seal around the well where the well casing emerges from the ground to stop surface water running down the side of the well casing. 

Keep the well cap closed tightly to prevent surface water, animals or contaminants from getting into the well. Make sure that your well also has a backflow preventer which will stop pumped water flowing back into your well.

We also recommended that you filter and treat well water before you drink it. Well water can easily be tainted by contamination sources hundreds of metres away from the well.

You can find more useful resources in this pamphlet from the Ministry of Health and from the HealthEd website

1. Well cap - tightly installed and sealed between the casing and any hoses/cabling going down into the well

2. Well casing - ensure casing is above any potential flooding

3. Concrete apron - seals the casing and the surrounding ground. The seal should slope away from the bore to stop surface water pooling around the bore casing. There may also be a bentonite seal around the casing, depending on the drilling method used

4. Backflow preventer - stops contaminants siphoning back into your well

5. Sample point - it would be useful for your well to have a sample point


1. Store rubbish, pesticides, compost, fertilisers and petro-chemicals near a well head

2. Locate offal pits, septic tanks and other contaminant sources near any well


1. Keep the area around the well clear of animals (e.g. via fencing around the area), pesticides, fertilisers, compost, rubbish, vegetation and effluent

2. Have a raw water sample point so you can quickly test the water. This will help if you need to check whether contamination is at the well, a treatment system failure or is a contamination in the pipes leading to drinking water taps

3. Maintain the well - earthquakes and ground movements can damage a well head

4. Look into the history of your land in case any existing or historical activites nearby may affect well water quality

5. Find out how your well has been constucted and operates so that you can preserve it. Ask your regional council or driller for more information

Well construction – in particular it's worth finding out:

  • When the well was drilled,
  • What geology the well is located in,
  • How deep the well is,
  • How it was constructed,
  • The type of pump and depth at which it is set within the well,
  • Information on the pumping rate and water level drawdown

These details are recorded in a driller’s log prepared at the time the well was drilled and will help you understand where water is coming from, what type of geology it flows through, and if the well has been constructed correctly to prevent contamination from entering the well. 

 Unwanted wells must be properly decomissioned or sealed to prevent contamination entering groundwater. 

If you do not decommission an unwanted bore on your property you can be fined.  Your local driller can provide advice on decommissioning and keeping your well secure.

2. Stream, river, or spring 

It can be hard to prevent streams, rivers and springs becoming contaminated by factors further upstream that you don’t know about.

To reduce bacteria risk to your surface water supply collect your water as close as possible to origin of your source. For example in headwaters of a river or stream where there are less impacts from humans or animals.  Fence off the area surrounding your water collection point to stop animals from entering your water supply.

Because streams, rivers and springs are easily accessed by animals or impacted by upstream activities, we recommend that you filter and treat water before drinking.

You can find more information on the HealthEd website


3. Roof rainwater collection tank water

We encourage you to:

  • Read the Ministry of Health's guidelines on how to correctly install and protect roof rainwater collection supplies
  • Check your roof has been painted with lead-free paint and does not have lead flashings
  • Check your collection system has gutter mesh, plastic pipe, and gutters approved for rainwater collection
  • Keep your water tank covered and trim all vegetation overhanging your roof to stop animals, leaf litter, and debris from accessing the tank and roof
  • Have your tank inspected annually and if necessary cleaned by a qualified tank cleaner

 Testing and treating your water supply for safe use

It's your responsibility to ensure the water is safe before use.

A lot of contaminants aren't visible, so regularly get your water tested to ensure it is safe to use. If there are changes in water colour, odour, taste or a sudden cloudy appearance, get it tested again, as it could suggest that your water is contaminated and unsafe to use. 

The best way to check for potential water quality issues is to collect a water sample and have this tested by an independently accredited IANZ laboratory. 

Every drinking water supply should be tested annually at a minimum to make sure it is safe to use. 

You will need to consult a qualified water treatment expert on water treatment options that are appropriate for your water supply. 

Visit International Accreditation New Zealand (IANZ) for any information on testing and for a list of Ministry of Health accredited laboratories that may be able to test your water supply. 


Where can I go for more information?

The Ministry of Health

Contact your District Council of Public Health Unit for advice on:

  • Health and concerns about changes in water that you see
  • Water sampling and quality testing
  • Interpretation of water test results
  • Compliance with NZ Drinking Water Standards
  • Advice on water treatment options
  • Historical land use and potential contaminated land issues

Contact our environmental science team for advice on:

  • Well siting
  • Well construction
  • Groundwater quality data
  • Availability of groundwater and surface water
Queries can be sent to

1.     Well cap –tightly installed and sealed between the casing and any hoses/cables going down the well.

2.     Well casing – ensure casing is above any potential flooding.

3.     Concrete apron –seals the casing and the surrounding ground. The seal should slope away from the bore to stop surface water pooling around the bore casing. There may also be a bentonite seal around the casing, depending on the drilling method used.

4.     Backflow preventer –stops contaminants siphoning back into your well.

5.     Sample point – it would be useful for your well to have a sample point.