Nitrates - Lower Waihao
What are nitrates and how are they measured?
Nitrate exists naturally in soil from the breakdown of organic matter and is also added through animal urine and fertilizer that has dissolved and has not been absorbed by the plants. If nitrate transfers into a water supply and is above 50 mg/L nitrate (NO3), the water will not meet drinking water standards for health.
Nitrate is a water soluble molecule made of nitrogen and oxygen. It is formed when nitrogen from ammonia or another source combines with oxygenated water. Nitrate is naturally found in plants and many foods, and is tasteless and odourless. Consequently it is naturally occurring in the environment, but also can enter the environment by other pathways including, but not limited to, chemical fertilisers and various land uses.
Nitrate values are commonly reported as either:
• Nitrate-N = nitrate nitrogen (NO3-N), used by the Laboratories
• Nitrate-NO3 = nitrate (NO3) is used in the New Zealand Drinking Water Standards
1 mg/L of Nitrate-N (nitrate nitrogen [NO3-N]) = 4.43 mg/L of Nitrate-NO3 (nitrate [NO3])
Council continue to undertake regular sampling at the water source, with these samples independently tested by an accredited laboratory. Council also has an online nitrate probe to monitor the nitrate levels in real-time, so simply put, we are keeping very close tabs on the situation.
Public health advice
Around the world nitrate levels in water sources have increased as a result of agricultural intensification, which has led to increased nitrate contamination of drinking water. High levels of nitrate in drinking water do pose a health risk to the youngest members of our community.
The most at-risk groups are formula-fed babies under the age of six months, and unborn foetuses who can be affected by their pregnant mother drinking water with high nitrate levels. There may be a risk to adults with specific rare metabolic disorders, but most healthy adults and older children are considered lower risk. Fully breastfed infants are not at risk as nitrate does not transfer into breast milk.
When nitrate enters our gut, bacteria in our system converts it into nitrite. Young babies and unborn foetuses have a unique oxygen-carrying protein molecule called foetal haemoglobin, and nitrite combines with this haemoglobin, stopping oxygen from binding to the molecule and being sent around the body.
If your baby has blueness around the mouth, hands and feet it could be a sign they have what is called “blue-baby syndrome.” If you note these symptoms or are at all concerned, please seek medical advice immediately. Thankfully there have been few reported instances of “blue-baby syndrome” here in New Zealand.
New Zealand’s drinking water standards set a maximum acceptable level of 50mg/l for nitrate. The levels in the Lower Waihao Rural Water Scheme are currently elevated at 42mg/l nitrate, and while this is close to the limit it is still considered safe to drink. However, scheme users are advised to make use of the safe water stations provided by Waimate District Council to eliminate any risk.
This is even more important for our at-risk groups, namely pregnant women and formula-fed infants under six months old. To keep themselves safe they must use another source of water for drinking and making up formula.
Some recent epidemiological evidence suggests a link between nitrate in drinking water and increased cancer risk, particularly colorectal cancer. However, research is ongoing into this link and it's not possible to give definitive advice about it at this time.
Dr. Matthew Reid
South Canterbury Medical Officer of Health
Animal health advice
There is no enforceable drinking water standard for livestock in New Zealand, however it is recommended that animals do not drink water with more than 443 mg/l Nitrate-NO3, according to the Colorado State University (CSU). This is especially true of young animals, as they are affected by nitrates the same way as human babies. Older animals may tolerate higher levels.
Ruminant animals (cattle, sheep) are susceptible to nitrate poisoning because bacteria present in the rumen convert nitrate to nitrite. Non-ruminant animals (swine, chickens) rapidly eliminate nitrate in their urine. Horses are monogastric, but their large cecum acts much like a rumen. This makes them more susceptible to nitrate poisoning than other monogastric animals.
However, currently the Lower Waihao Rural Water Scheme level is 42 mg/L of Nitrate-NO3. This is only 9.5% of the recommendation, and therefore the risk to livestock is virtually nil. So an alternate source of water is unlikely to be required. Therefore:
- No issues with adult or younger weaned stock drinking the water at the current nitrate levels
- For calves on whole milk with access to drinking water at the current levels, it is safe
- For farms using the water to mix milk powder for feeding to this seasons calves at the current levels, it is fine to continue
- Those using the water to mix milk powder for feeding to this seasons lambs should proceed with caution, but at the current levels it should be safe.
In New Zealand there has been no recorded cases of methaemoglobinaemia in stock associated with drinking water.
As for smaller animals such as cats and dogs (pets), we recommend household pets be given potable drinking water. While cats and dogs can handle a higher level of nitrates than most people, it’s advisable to err on the side of caution when providing their water intake.
We also advise those with any fish tanks that they monitor the water quality. Nitrate levels in fish tanks should be less than 20 mg/L to keep fish healthy, however nitrate toxicity to fish varies depending on species, age and overall health.
We recommend that you keep quick test strips or a test kit that uses chemical reagents on hand to monitor nitrate levels in your fish tank closely.
To assure water quality is safe for fish, either source water without high nitrate levels, or use fish water tank conditioner to detoxify nitrates. Please follow supplier directions on use (not for human consumption). For further advice talk to your pet store or vet.
If you have questions about the advice on this page, or concerns not covered, please contact your local veterinarian.
Ryan Luckman BVSc (Dist)
MANZCVS (Epidemiology)
VETERINARIAN
Public meeting
On September 10 2022, Council hosted a public meeting at the Glenavy Hall. As part of the solution, Council are working closely with Taumata Arowai and Environment Canterbury to resolve this issue at the earliest opportunity, but there are a number of factors to consider and this will take time.
Those that attended the meeting included residents, Council staff, South Canterbury Medical Officer of Health Dr Matthew Reid, Environment Canterbury representatives and community stakeholders.
Future meetings
We also plan to hold another public meeting once the treatment plant upgrade has further progressed. We will advertise this meeting on the Council website, Facebook page and the local Waimate Trader.
Denitrification plant project
What are we doing?
Currently we are completing a treatment plant upgrade at the Lower Waihao intake, with an addition of a denitrification treatment process.
The upgrade for the Lower Waihao Rural Water Scheme Treatment Plant was already underway and budgeted for in our Long Term Plan, at the time of the event. A preliminary design for denitrification process at the plant had been a part of the main design. This preliminary plan is now being refined and costed, and now will be a part of the new plant upgrade.
When will the new treatment plant be commissioned?
We are anticipating the plant to be commissioned in May or June 2023.
How do you plan to treat the nitrates?
The denitrification system chosen is an Ion-exchange process .The treatment process will include 4x filter units. It will be a modular system where more filter units can be attached if required in the future. The system will be initially specified to remove up to 80 mg/L Nitrate-NO3.
Ion exchange systems are used for efficient removal of dissolved ions from water, like nitrates. Ion exchangers exchange one ion for another, hold it temporarily, and then release it to a re-generation solution. In an ion exchange system, undesirable ions like nitrates in the water supply are replaced with more acceptable ions.
Why do we have to do this?
As a water supplier we are obligated to provide safe drinking water. The planned upgrade was to meet drinking water standards and the additional denitrification process is to bring the nitrates to a compliant level.
Where is the new treatment plant located?
It is located close to the current treatment plant, however we have now placed the plant on an elevated area to prevent future flood risk.
How much will the treatment plant cost?
We do not have final costings at this stage. A treatment plant upgrade was already in our long term plan with a budget of $1.8 million. The only additional costing we are expecting relates to the denitrification process.
Have we looked at an alternative source?
Yes. There have been seven attempts to find an alternative source which all have been unsuccessful, with no other real viable options.
Regular updates
Frequently asked questions
Can I shower and bathe in the water?
Yes, nitrates in water only affect you if digested, do not use the water for food preparation or drinking, but you can bathe, wash your clothes and flush your toilet with the water.
Where does the water for the water tank stations come from, and is it safe?
The water in all four potable water tank stations (Morven, Glenavy, Glenavy School, and Glenavy Fishing Huts) is compliant with the New Zealand Drinking Water Standards and is safe. It is chlorinated, and staff monitor the free available chlorine levels weekly along with bacterial monitoring (E.coli & Total coliforms), to assure the drinking water is safe and compliant. The tanks are also topped with fresh water fortnightly.
The drinking water supplied to the tanks is delivered by a registered drinking water carrier that comes from Temuka Transport. This means the water supplied so far has currently come from Temuka township, which is also a compliant registered drinking water supply in the Timaru District. Both the source and transport of water meet the current New Zealand Drinking Water Standards requirements.
Why is there a water station on Hillary Street in Waimate?
Council have this water station available for the convenience of the Lower Waihao (including Waikakahi East) scheme users who are regularly in Waimate. This water comes directly from the Waimate township water supply.
What if I have difficulty getting to, or collecting the potable water from the council water station tanks?
If you or someone you know has difficulty accessing these locations, please contact Council on 03 689 0000.
Will those on the scheme be required to replace their point of supply storage tanks?
No, you will not need to replace your point of supply storage tanks. We are still working through how best to deal with the water at point of supply storage tanks once the denitrification processes are in place. We would look at options such as cycling the water i.e normal draw off and replenishment with compliant drinking water over a period of time. This is yet to be determined.
What about my pets?
During this nitrate advisory, we recommend household pets be given the potable drinking water. While dogs and cats can handle a higher level of nitrates than most people, it’s advisable to err on the side of caution when providing their water intake.
If you have any further queries or issues relating to animals, please speak with your local vet.
Should I be testing my private bore?
Yes, Environment Canterbury and Council recommend anyone who takes their drinking water from a private bore undergoes regular water quality testing to ensure the safety of their drinking water. There is also raised concern as we know of our own nitrate issue. Nitrate is tasteless so your water may be affected even if you haven’t found any noticeable change in taste.
Environment Canterbury provides further advice on this here; https://www.ecan.govt.nz/your-region/your-environment/water/whats-happening-in-my-water-zone/ashburton-water-zone/action-on-the-ground/protecting-your-private-drinking-water-source/
Additional resources
Understanding nitrate exceedance
Environment Canterbury (ECan) is supporting Waimate District Council to help resolve the nitrate exceedance at its Lower Waihao Rural Water Supply in the Glenavy and Morven area with technical advice and additional monitoring of land use activities in the area. To learn more about ECan's involvement, click below.
Protecting your private drinking water source
Testing private wells is the owner’s responsibility. It should be undertaken at least four times per year for E. coli, as well as annually for nitrate.
ECan has produced a brochure with practical information about how to protect your well head.
Click HERE to download a copy.
