Private drinking water supplies
If your drinking water comes from a private supply (such as a well or a surface source) there are things you need to know to keep you, your family, and those working on your land safe.
Drinking water can be contaminated by bacteria (such as E. coli), viruses, nitrate, metals and chemicals. Some contaminants occur naturally, while others come from human activities.
Test your water supply
The best way to ensure your self-supplied drinking water is safe is to test it regularly and make sure the source of the supply is protected and maintained.
Testing is easy to do:
- Decide what to test for: Consider a basic test for E. coli or nitrate and/or something more comprehensive, such as heavy metals and/or organic chemicals.
- Order a testing kit from an accredited (IANZ) testing lab: Visit the Water Services Authority - Taumata Arowai for a list of accredited labs.
- Take a sample: Follow the instructions that come with the kit. Taking a sample directly from the tap is usually sufficient.
- Send to the lab: Pack the sample, as instructed, and send back to the lab right away.
Contaminants to test for and how often
Contaminants that can be found in your water can fit into three categories: pathogens (bugs), nitrate, and heavy metals and chemicals.
Pathogens (bugs)
Recommended test frequency: every three months
Pathogens, such as viruses or bacteria can come from faecal material from grazing animals or animal or human effluent storage and disposal.
E.coli is an indicator of faecal contamination. You should test for E. coli quarterly, especially following heavy rainfall.
Drinking Water Standards for NZ 2022 state that the maximum acceptable value for E.coli is less than 1 in 100 mL of sample.
Seek specialist advice on treatment options for pathogens to keep your drinking water safe. Methods could include one or a combination of ultraviolet disinfection, chlorination, and filtration. As an interim solution, boiling water for one minute will destroy most pathogens.
Nitrate
Recommended test frequency: annually
Nitrate can enter groundwater from farming activities, usually through animal urine and fertilisers, as well as from wastewater disposal and landfills. It can remain in the subsoil during dry periods and seep into groundwater following significant rainfall.
We recommend testing nitrate levels annually, preferably during spring or autumn when nitrate levels tend to be higher. You should flush the tap for two to three minutes before sampling.
Drinking Water Standards of NZ 2022 state that the maximum acceptable value for nitrate is 11.3 mg/L of nitrate-nitrogen (sometimes expressed as 50 mg/L of nitrate)
Water with nitrate above the maximum acceptable value should not be used to prepare formula for young babies. Pregnant women and parents of new babies should talk to their lead maternity carer about the risks.
Nitrate levels can spike after heavy rainfall, especially if that rainfall follows a long dry period. These nitrate spikes are greatest in shallow wells. Boiling or filters do not remove nitrate from the water.
If your water requires treatment for nitrate, seek specialist advice. Methods could include reverse osmosis or ion exchange.
Heavy metals and organic chemicals
Recommended test frequency: once
Heavy metals include cadmium, lead, manganese and arsenic. Organic chemicals include petroleum compounds, industrial solvents and pesticides.
These contaminants can come from a variety of sources including old sheep dips, landfills and industry.
The Listed Land Use Register (LLUR) is a publicly available database of sites where hazardous activities and industries have been located throughout Canterbury. This can help you identify whether any of these activities have been carried out on or near your property.
Arsenic and manganese also occur naturally in the sediments in some parts of Canterbury and can reach harmful levels in groundwater, especially if the water is low in oxygen. If a water supply has a bad odour (smells like rotten eggs or sour cabbage) or high iron levels causing rusty staining where it comes into contact with air, these are signs that the water is low in oxygen and it is advisable to test for arsenic and manganese.
A test for a full range of heavy metals and organic chemicals can be expensive, but only needs to be done once, unless you notice a change in the water.
Boiling or filters do not remove dissolved heavy metals from the water. Seek specialist advice if your water requires treatment for heavy metals or organic contaminants.
Treat your water if necessary
If you are concerned about the quality of your water supply, or if testing shows that the water does not meet drinking-water standards, you may need to consider treating the water.
Water treatment is complex and requires specialist advice specific to an individual supply. Public Health and Forensic Science (PHF Science) has produced a comprehensive guide to household water supplies.
Protect your water supply
Protect your well head
The point where a well emerges from the ground is known as the well head (or bore head). Protecting this is important to prevent harmful microbes and substances from contaminating your water.
We recommend that your well is as far away as practical from potential sources of contamination, such as compost, rubbish, septic tanks, offal holes, and effluent disposal areas.
You should check and inspect your well head regularly to ensure:
- the area immediately around the well head is well clear of animal stock and effluent, pesticides, fertiliser, compost, rubbish, or stormwater
- adequate drainage to prevent ponding around the wellhead
- the well casing is elevated above the ground (at least half a meter) and that the seal, well cap, casing, and apron are intact
- pumps are not leaking oil or grease
Get more detailed advice for protecting your well head
Visit the Water Services Authority - Taumata Arowai for comprehensive information on: drinking water testing and treating; protecting the water source; and responsibilities of water suppliers.